The instruments
शङ्कु · नाडिका · वर्षमानम् · गोलयन्त्र
The first three essays read observations and arguments — stars watched, a frame that drifted, a shadow explained. This one reads hardware. The instruments of early Indian astronomy were made of cord, clay, water and cloth, and not one physical example survives; what survives is something arguably better — the specifications. A gnomon defined by its shadow-geometry, a water-clock defined by its fill-measure, a rain gauge defined by its aperture, a globe defined by what it must demonstrate: four instruments, each quoted below from the text that specifies it.
Every quote is a verbatim slice from Jñānakośa, the research database behind this atlas; each links to its revision-pinned source page. Translations are literal renderings; dates are approximate spans of compilation. Display markup of the e-texts is removed here — the full text, apparatus and confidence grades are one click away.
What can be measured
मूर्तः कालः · time you can hold
Before the instruments, the doctrine of what they measure. The Sūrya-siddhānta opens by splitting Time in two: the Time that destroys worlds, and the Time that can be reckoned — and it splits the reckonable again, at exactly the point where instruments begin. Below the breath (prāṇa, about four seconds), time is amūrta, 'unembodied' — real but uninstrumentable. From the breath upward, time is mūrta, embodied: six breaths a vināḍī, sixty of those a nāḍī, sixty nāḍīs a day. The ladder's rungs are the dial-marks of everything that follows:
Sūrya-siddhānta 1.10–13 · c. 5th–8th c. CE
लोकानां अन्तकृत्कालः कालो +अन्यः कलनात्मकः । स द्विधा स्थूलसूक्ष्मत्वान्मूर्तश्चामूर्त उच्यते ॥ १.१० ॥ प्राणादिः कथितो मूर्तस्त्रुट्याद्यो +अमूर्तसंज्ञकः । षड्भिः प्राणैर्विनाडी स्यात्तत्षष्ट्या नाडिका स्मृता ॥ १.११ ॥ नाडीषष्ट्या तु नाक्षत्रं अहोरात्रं प्रकीर्तितम् । तत्त्रिंशता भवेन्मासः सावनो +अर्कोदयैस्तथा ॥ १.१२ ॥ ऐन्दवस्तिथिभिस्तद्वत्संक्रान्त्या सौर उच्यते । मासैर्द्वादशभिर्वर्षं दिव्यं तदह उच्यते ॥ १.१३ ॥
Time is the destroyer of the worlds; another Time has for its nature to bring to pass. This latter, according as it is gross or minute, is called by two names, real (murta) and unreal (amurta). That which begins with respirations (prana) is called real; that which begins with atoms (truti) is called unreal. Six respirations make a vinadi, sixty of these a nadi; and sixty nadis make a sidereal day and night. [1.12b–13, abridged in Burgess's printing, in the compiler's rendering:] thirty of those [make] a month; a civil (sāvana) month is by thirty sunrises; a lunar month likewise by tithis; by the saṃkrānti it is called solar. Twelve months are a year — and that is called a day of the gods.
East from a shadow
शङ्कु · a stick and a circle
The oldest instrument is a stick. The śulba manuals — the cord-geometry appendices of the ritual — need true east before they can lay a single brick, and the Kātyāyana text gives the procedure whole: level the ground, plant the gnomon (śaṅku), draw a circle around it with a cord, mark where the shadow-tip crosses the circle in the morning and again in the afternoon. The line between the marks is east — by symmetry, with no sighting of the sunrise at all:
Kātyāyana-śulbasūtra 1.1–3 · c. 400–200 BCE
रज्जुसमासं वक्ष्यामः १
समे शङ्कुं निखाय शङ्कुसम्मितया रज्ज्वा मण्डलं परिलिख्य यत्र लेखयोः शङ्क्वग्रच्छाया निपतति तत्र शङ्कू निहन्ति सा प्राची । तदन्तरं रज्ज्वाभ्यस्य पाशौ कृत्वा शङ्क्वोः पाशौ प्रतिमुच्य दक्षिणायम्य मध्ये शङ्कुमेवमुत्तरतः सोदीची २
रज्ज्वन्तयोः पाशौ करोति । श्रोण्यंसनिरञ्छनसंख्यासमासभङ्गेषु लक्षणानि । प्राच्यन्तयोः शङ्कु निहन्ति । श्रोण्योरंसयोश्च । शङ्क्वोः पाशौ प्रतिमुच्य निरञ्छनेन गृहीत्वा दक्षिणपूर्वां दिशं हरन्ति । एवमुत्तरतः । विपर्यस्येतरतः । स समाधिः सर्वत्र ३
We shall declare the combination of the cord. Having planted a gnomon on leveled [ground] and drawn a circle with a cord measured by the gnomon, one plants stakes where the gnomon-tip's shadow falls on the line [in the forenoon and afternoon] — that is the east [line]. Stretching a cord of twice that interval with two loops, fastening the loops on the two stakes and drawing [it] south, [one plants] a stake at the middle; likewise to the north — that is the north [line]. [For the square:] one makes loops at the cord's ends; marks at the hip-, shoulder-, and slack-points … fastening the loops on the two east-line stakes, taking it by the slack-mark one draws toward the southeast; likewise to the north; the reverse on the other side. This is the method everywhere.
A thousand years on, the Sūrya-siddhānta opens its chapter on directions with the same procedure, now standardized — the gnomon fixed at twelve digits by convention, the two crossings refined through the fish-figure (matsya) construction that every Indian geometer drew to bisect a line. The stick has become a calibrated instrument with a canonical size:
Sūrya-siddhānta 3.1–4 · c. 5th–8th c. CE
शङ्क्वङ्गुलैरिष्टैः समं मण्डलं आलिखेत् ।। ३.०१ ।।
तन्मध्ये स्थापयेच्छङ्कुं कल्पनाद्वादशाङ्गुलम् ।
तच्छायाग्रं स्पृशेद्यत्र वृत्ते पूर्वापरार्धयोः ।। ३.०२ ।।
तत्र बिन्दू विधायोभौ वृत्ते पूर्वापराभिधौ ।
तन्मध्ये तिमिना रेखा कर्तव्या दक्षिणोत्तरा ।। ३.०३ ।।
याम्योत्तरदिशोर्मध्ये तिमिना पूर्वपश्चिमा ।
दिङ्मध्यमत्स्यैः संसाध्या विदिशस्तद्वदेव हि ।। ३.०४ ।।
On [ground made] level, one should draw an even circle with a radius of any desired gnomon-digits; at its center set the gnomon, twelve digits by convention. Where the tip of its shadow touches the circle in the forenoon and afternoon halves, there make two points, called the east and the west. Between them, with the fish[-figure], a line is to be made, the south-and-north; between the south and north directions, [a line] east-and-west by the fish; and the intermediate directions likewise, by the fishes between the direction-[points].
See: the Kṛttikās' east in essay two
Time by water
नाडिका · the bowl that drinks the day
Night, cloud, and the spaces between observations need a clock that runs without the sun. The Vedāṅga-jyotiṣa — the Veda's astronomy manual — defines its unit vessel by fill: fifty palas of water make an āḍhaka, from which the droṇa is measured out, and the droṇa less three kuḍavas is the nāḍikā — the water-measure of the clock that shares its name with the unit of time it drains in:
Vedāṅga-jyotiṣa, Yājuṣa 24 · c. 700–400 BCE
पलानिपञ्चाशदपांधृतानितदाढकंद्रोणमतःप्रमेयम्।
त्रिभिर्विहीनंकुडवैस्तुकार्यंतन्नाडिकायास्तुभवेत्प्रमाणम्॥२४॥
Fifty palas of water held — that is the āḍhaka; from that the droṇa is to be measured out. Diminished by three kuḍavas, that [droṇa] is to be made the measure of the nāḍikā.
And the same text uses its clock as a measuring instrument for the year itself: through the northward course the day grows by one prastha of water per day — daylight literally weighed, its seasonal swing summed to six muhūrtas over the half-year. A rate stated in clock-units is the signature of an instrument in daily use:
Vedāṅga-jyotiṣa, Ārca 7 · c. 700–400 BCE
धर्मवृद्धिरपाम्प्रस्थःक्षपाहासउदग्गतौ।
दक्षिणेतौविपर्यस्तौषण्मुहूर्त्ययनेनतु॥७॥
In the northward course, the increase of the day is a prastha of water, and the shrinkage of the night [the same]; in the southern course the two are reversed; and by the [full] ayana, [the change] is six muhūrtas.
The Bhāgavata carries the full metrological ladder — from the paramāṇu, through the trasareṇu ('the mote seen climbing a sunbeam through a lattice': the smallest observable, honestly chosen), up through the blink and the count to the moment the scale touches hardware again. Purāṇic time is often quoted for its immense yugas; the same chapter's lower rungs are a working clock spec:
Bhāgavata-purāṇa 3.11.5–9 · c. 500–1000 CE
aṇur dvau paramāṇū syāt trasareṇus trayaḥ smṛtaḥ / jālārka-raśmy-avagataḥ kham evānupatann agāt // bhp_03.11.005 // trasareṇu-trikaṃ bhuṅkte yaḥ kālaḥ sa truṭiḥ smṛtaḥ / śata-bhāgas tu vedhaḥ syāt tais tribhis tu lavaḥ smṛtaḥ // bhp_03.11.006 // nimeṣas tri-lavo jñeya āmnātas te trayaḥ kṣaṇaḥ / kṣaṇān pañca viduḥ kāṣṭhāṃ laghu tā daśa pañca ca // bhp_03.11.007 // laghūni vai samāmnātā daśa pañca ca nāḍikā / te dve muhūrtaḥ praharaḥ ṣaḍ yāmaḥ sapta vā nṛṇām // bhp_03.11.008 // dvādaśārdha-palonmānaṃ caturbhiś catur-aṅgulaiḥ / svarṇa-māṣaiḥ kṛta-cchidraṃ yāvat prastha-jala-plutam // bhp_03.11.009 //
Two paramāṇus make an aṇu; three [aṇus] are held to be a trasareṇu — that which is perceived moving up through the sky in a sunbeam through a lattice. The time that passes over three trasareṇus is called a truṭi; a hundred of those a vedha; three vedhas a lava. Three lavas are to be known as a nimeṣa (a blink); three of those a kṣaṇa; five kṣaṇas a kāṣṭhā; fifteen of those a laghu; fifteen laghus are declared a nāḍikā; two of those a muhūrta; six or seven [muhūrtas] a prahara, a watch of men. [The nāḍikā's gauge:] a vessel measuring six palas, pierced by a four-māṣa gold [probe] four aṅgulas long, [sinks] when flooded by a prastha of water.
Rain by the droṇa
वर्षमानम् · the fiscal sky
The Arthaśāstra's storehouse chapter specifies an instrument in nine words: set up, in the granary compound, a varṣamāna — a 'rain-measure' — a bowl whose mouth is one aratni across. The fixed aperture is the entire technology: with the mouth standardized, the depth collected is comparable between stations and seasons, and rain becomes a number:
Arthaśāstra 2.5.7 · c. 300 BCE – 300 CE
कोष्ठ-अगारे वर्षमानं अरत्नि-मुखं कुण्डं स्थापयेत् ।। ०२.५.०७ ।।
In the storehouse [compound] let him set up a rain-measure (varṣamāna), a bowl with a mouth of one aratni.
And the numbers were kept. The rainfall book of the same text states normals by region — sixteen droṇas for the dry lands, twenty-three for Avantī, 'immeasurable' on the western coast — and the shape of a good monsoon across the season, with forecasting rules to match. A gauge at the granary and a table of normals is agro-meteorology run as fiscal policy:
Arthaśāstra 2.24.5–10 · c. 300 BCE – 300 CE
षोडश-द्रोणं जाङ्गलानां वर्ष-प्रमाणम् । अध्यर्धं आनूपानां देश-वापानाम् । अर्ध-त्रयोदशाश्मकानाम् । त्रयोविंशतिरवन्तीनाम् । अमितं अपर-अन्तानां हैमन्यानां च । कुल्या-आवापानां च कालतः ।। ०२.२४.०५ ।। वर्ष-त्रि-भागः पूर्व-पश्चिम-मासयोः । द्वौ त्रि-भागौ मध्यमयोः सुषमा-रूपं ।। ०२.२४.०६ ।। तस्यौपलधिर्बृहस्पतेः स्थान-गमन-गर्भ-आधानेभ्यः शुक्र-उदय-अस्तमय-चारेभ्यः सूर्यस्य प्रकृति-वैकृताच्च ।। ०२.२४.०७ ।। सूर्याद्बीज-सिद्धिः । बृहस्पतेः सस्यानां स्तम्ब-कारिता । शुक्राद्वृष्टिः इति ।। ०२.२४.०८ ।। त्रयः सप्त-अहिका मेघा अशीतिः कण-शीकराः । ।। ०२.२४.०९अ ब ।। षष्टिरातप-मेघानां एषा वृष्टिः समा हिता ।। ०२.२४.०९च्द् ।। वातं आतप-योगं च विभजन्यत्र वर्षति । ।। ०२.२४.१०अ ब ।। त्रीन्करीषांश्च जनयंस्तत्र सस्य-आगमो ध्रुवः ।। ०२.२४.१०च्द् ।।
Sixteen droṇas [of rain] is the rain-measure of the dry (jāṅgala) lands; half again as much for the wet lands sown by broadcast(?); thirteen and a half for the Aśmakas; twenty-three for the Avantis; unmeasured for the Aparāntas and the snowy [lands]; and for canal-sown lands, according to season. A third of the rain in the first and last months, two three-part shares in the two middle ones — that is the form of a good year (suṣamā). Its ascertainment [comes] from Jupiter's stations, movements, and occultations(?), from the risings, settings, and courses of Venus, and from the natural and altered appearances of the sun. From the sun, the success of the seed; from Jupiter, the stem-formation of the crops; from Venus, rain. Three seven-day rains, eighty of drops-and-drizzle, sixty of rain-with-sunshine — this rain is even and beneficial. Where it rains apportioning wind and sunshine, and making three [wettings?], there the coming of the crop is sure.
The globe that turns itself
गोल · the working model
The last instrument is a model of everything. Āryabhaṭa states what any true model must show: globes are half-lit by the sun and half-darkened by their own shadow, and the earth-globe hangs in the middle of space, in the middle of the cage of the asterisms — 'like a kadamba blossom, covered with creatures on all sides':
Āryabhaṭīya, Gola 5–7 · 499 CE
भूग्रहभानां गोल अर्धानि स्वछायया विवर्णानि । अर्धानि यथासारं सूर्याभिमुखानि दीप्यन्ते ।। ४.५ ।। वृत्तभपञ्जरमध्ये कक्ष्यापरिवेष्टितस्खमध्यगतस् । मृद्जलशिखिवायुमयस्भूगोलस्सर्वतस्वृत्तस् ।। ४.६ ।। यद्वत्कदम्बपुष्पग्रन्थिस्प्रचितस्समन्ततस्कुसुमैस् । तद्वत्हि सर्वसत्त्वैस्जलजैस्स्थलजैस्च भूगोलस् ।। ४.७ ।।
Half of the globes of the earth, the planets, and the asterisms are darkened by their own shadows; the [other] halves, facing the sun, shine in proportion [to their position]. In the middle of the circular cage of the asterisms, wreathed about by the orbits, in the middle of space, stands the globe of the earth — made of earth, water, fire, and air — wholly round. As the bulb of a kadamba blossom is covered on all sides by its flowers, just so is the globe of the earth [covered] by all creatures, water-born and land-born.
The Sūrya-siddhānta builds it. Its sphere-instrument (gola-yantra) is wrapped in cloth, ringed by the horizon of Lokāloka, and driven — made 'an instrument of the revolution of time' by flowing liquid, with mercury named among the movers. Then comes the most consequential sentence in the history of Indian instrumentation: the operative secret (bīja) is गोप्यम् — to be guarded, 'for spoken openly it would become common to all'. The drive mechanisms died with their guilds; the specification survived because the text kept it:
Sūrya-siddhānta 13.16–22 · c. 5th–8th c. CE
वस्त्रच्छन्नं बहिस्चापि लोकालोकेन वेष्टितम् ।
अमृतस्रावयोगेन कालभ्रमणसाधनम् ॥ १३.१६ ॥
तुङ्गबीजसमायुक्तं गोलयन्त्रं प्रसाधयेत् ।
गोप्यं एतत्प्रकाशोक्तं सर्वगम्यं भवेदिह ॥ १३.१७ ॥
तस्माद्गुरूपदेशेन रचयेद्गोलं उत्तमम् ।
युगे युगे समुच्छिन्ना रचनेयं विवस्वतः ॥ १३.१८ ॥
प्रसादात्कस्यचिद्भूयः प्रादुर्भवति कामतः ।
कालसंसाधनार्थाय तथा यन्त्राणि साधयेत् ॥ १३.१९ ॥
एकाकी योजयेद्बीजं यन्त्रे विस्मयकारिणि ।
शङ्कुयष्टिधनुश्चक्रैश्छायायन्त्रैरनेकधा ॥ १३.२० ॥
गुरूपदेशाद्विज्ञेयं कालज्ञानं अतन्द्रितैः ।
तोययन्त्रकपालाद्यैर्मयूरनरवानरैः ॥
ससूत्ररेणुगर्भैश्च सम्यक्कालं प्रसाधयेत् ॥ १३.२१ ॥
पारदाराम्बुसूत्राणि शुल्वतैलजलानि च ।
बीजानि पांसवस्तेषु प्रयोगास्ते +अपि दुर्लभाः ॥ १३.२२ ॥
[The sphere-frame,] covered with cloth, girded outside by [the ring of] Lokāloka, [is made] an instrument for the revolution of time by the application of flowing liquid. Joined with its elevation and its bīja [operative secret], one should accomplish the sphere-instrument. This, spoken openly, would become common to all — therefore let one build the excellent globe by the teacher's instruction. In age after age this construction of the Sun perishes, and by someone's grace it comes forth again; so let him accomplish the instruments for the reckoning of time. ALONE let him join the bīja to the wonder-working instrument. With gnomon, staff, bow, and wheels, with shadow-instruments of many kinds; with water-instruments, the bowl and the rest, with peacock, man, and monkey [figures], and with those bearing cords and sand within — let him establish time correctly. Mercury-holes(?), water, cords, copper and oil and water, sands — these are the bījas among them; and their applications are hard to obtain.
See: the shadow it demonstrates
गोप्यम् — to be guarded
Four instruments, four materials — wood, water, clay, cloth — and four survivals by text alone. The secrecy clause explains the archaeology: an instrument whose operating principle is a guild secret is an instrument nobody writes a maintenance manual for, and when the guild ends, the hardware ends with it. What the tradition chose to preserve instead was the part that cannot rot: the aperture in aratnis, the gnomon in digits, the fill in palas, and the demand — stated outright in the trepidation and eclipse chapters quoted in the earlier essays — that the model be made to agree with what is seen.
Each quote carries its full citation and confidence grading in Jñānakośa (batch varshamana-pass1 joined the standing astronomy passes for this essay). And one instrument outlived the rest by changing its material: the sphere the texts call bhagol, the star-globe, is the name and the ancestor of the companion app — whose gol-yantra layer still draws the rings of the sphere-frame over the live sky, cloth and mercury no longer required.