The description and use of the nocturnal by M. Samuel Foster ... ; with the addition of a ruler, shewing the measures of inches and other parts of most countries, compared with our English ones ; being useful for all merchants & tradesmen.

The Description and Use of the NOCTURNAL; By M•…•… Samuel Foster, late Reader of Astronomy in Gresham-Col∣ledge.

With the Addition of a Ruler, shewing the Measures of Inches and other Parts of most Countries, compared with our English ones; Being useful for all Merchants & Tradesmen.

THIS Nocturnal is made of two Plates; the thick Plate (which I call the Mater) and a Moveable Plate, representing the Aequinoctial. On the Mater, the Circle doth represent the Eccliptick. All the rest of the Writing, is the Names of as many of the Fixed Stars as the bigness of the Instrument will give leave. To these must be added an Index or Label, fastned at the Center, to cut the several Circles upon the Instrument.

The Use of the Nocturnal.

1. SET the Label to the Sun's Place in the Zodiack, and the Hour of Twelve in the Aequinoctial to the Star, whose time of coming to the Meridian you enquire after; and then look what hour and minute is cut by the Label in the Aequinoctial, for that is the hour of the Day or Night that the same Star will come to the South Part of the Meridian.

But you must observe, that the hours are marked in the Aequinoctial in this manner, 12, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11. Now the Difficulty lyeth, in finding whether the minutes you shall find cut by the Label in the Aequinoctial, doth be∣long

to the upper row of hours, Viz. 12, 1, 2, 3, 4 5, or to the under row, Viz. 6, 7, 8, 9, 10, 11; and whether from Noon, or from Midnight: In order to this you must know in what Sign the Star is that you observe, and take notice how far it is distant from the Place where the ☉ is that day; if it be not above three whole Signs, the Minute cut by the Label, belongeth to the upper row of hours to be accounted from Noon; and if the Distance of the Star, and of the ☉ be four, five, or six Signs, then the said Minute cut by the Label belongeth to the under row of hours, ac∣counted also from Noon: but if the Distance of the ☉ and Star be 7, 8, or 9 Signs, then the Minute belongeth to the upper row of hours accounted from Midnight. Lastly, if the Distance of the ☉ and Star be 10, 11, or 12 Signs, then the Minute belongeth to the under row of hours, accounted from Midnight. All which beforesaid shall be made clear by Examples.

Example the first. The ☉ being in the begin∣ning of ♌; when will Spica ♍ come to the Meridian? Set the Label to the beginning of ♌, and the hour 12 in the Aequinoctial to Spica ♍ then will the Label cut the 59th. Minute after 4, or after 10; now this Star being in ♎, which is not above three Signs from ♌, it must be after 4 of the Clock from Noon. I conclude then that the ☉ being in the beginning of ♌, the Spica ♍ will come to the South at 4^h. 59′ past Noon.

Example II. When will the same Star come to the Meridian, the ☉ being in the 10th. degree of ♊? The Label being set to the 10 of ♊, and 12 to the Star, as be∣fore, the Label shall cut the 35 Minute after 2 or 8; now it must be after 8, because the ☉ is above three Signs di∣stant from the Star, and yet not seven Signs; so Spica ♍ will come to the Meridian at 8^h. 35′ past Noon.

Example III. When will the same Spica ♍ come to the Meridian, the ☉ being in ♓ the 5th. Degree?

The Label being set to the 5° of ♓, shall cut 41′ after 2, or 8; but it must be 2, and after Midnight past, because the distance of the ☉ and the Star is above six whole Signs, and not nine.

Example IV. Working after the same manner, you will find that the same Star will come to the Meridian at 9h. 58′ past Midnight, the ☉ being in the 20° 00′ of ♏. I take the lower row of hours, and say, that 'tis after Mid∣night, because the ☉ is above nine Signs distant from the Star. NB. These Precepts are fitted to an Instrument made for 1671.

Additions to the Instrument, in Brass; made by Mr. R. Aug. 1st. 1684.

Calculated for the Year 1700, which will make some little difference in the aforesaid Precepts.

IF in this Instrument you set down to the several Stars their respective several Declinations, and by adding either an A, or B, according to the Declination of ei∣ther Austral or Boreal, you shall have the height of the Star when it cometh to the Meridian, Viz. by adding the De∣clination to the height of the Aequinoctial, when the said Declination is Northward, and by taking the Declination from the height of the Aequinoctial when the Declination is Southward.

As for Example. Suppose I desire to know when Cor ♌ shall come to the Meridian, what will be his Altitude in the Latitude of London 51° 30′. The height of the Aequi∣noctial is 38° 30′, to which add the Stars North Declination, 13° 02′ 〈 math 〉〈 math 〉 the Summe is 51° 32′ the Alti∣tude required.

So the Altitude of the Spica ♍ in the Meridian will be found to be 28° 57′ in the same Latitude; for the height of the Aequinoctial is 38° 30′; from which take the Stars South Declination 9° 33′, the Remainder is 28° 57′.

I have so contrived this Instrument, that by making two little square holes in the Moveable Plate, the first sheweth you in what Sign the Star is, which is absolutely necessary to be known, to judge of the distance between the ☉ and the Star (as you have been taught before) and the second shews the Magnitude of the Star.

To know at any time proposed, what Point of the Ecclip∣tick is in the Meridian.

Suppose the ☉ to be in the beginning of ♉, I desire to know what Degree of the Eccliptick shall be in the Meridian at 15′ past Five in the Afternoon.

I lay the hour given to the Sun's Place, and then I find over against the 12 a Clock line of the Aequinoctial, 15° 20′ of ♋; and that is the Degree that was then in the Me∣ridian.

To know when any of the Planets shall come to the Meridian.

The Planets, because of their continual changing of Place, cannot be set fixt in this Nocturnal: Nevertheless, if at any time you desire to know their time of coming to the Meridian, you must look in some Ephemeris for the Place of the Planet, and according as you find it, set it with Black-Lead on your Instrument, which if it be in Brass, shall be easily put out. The Planet thus set, shall be as a Fixed

Star, and its time of coming to the Meridian found out, as that of any of the Fixed Stars.

But Note, that if it be the Moon that you observe, you must allow about a degree for every two hours past since Noon; and thus you shall have her true Place; for the Ephe∣meris gives you her Place only at Noon.

For Example. When will the Moon come to the Meridi∣an on Ianuary the 1st. 168 4/5?

The ☉ is then in ♑ 22° 5′, and the Moon in ♈ 10° 12′. Now placing the Moon on my Instrument in ♈ 10° 12′, I find that the Moon shall come to the Meridian at a little past 5 in the Afternoon: and because there are five hours past since Noon, I must for these five hours allow two degrees and a half to the Moon's Place, and so set it to ♈ 13° 00′; which being done, I shall find the Moon's true hour of com∣ing to the Meridian, and that is at about 5h. 15′ past Five in the Afternoon.

Hitherto is the Instrument general to all those that live on this side the Aequioctial; and may serve to any Intelli∣gent Man that shall have South Declination.

But besides, I have made two little Windows in the Mo∣veable Plate, but the Figures of them are Calculated for the Meridian of London, or any other Place that is under the same Latitude of 51° 30′.

The first Window shews the Semi-Nocturnal Arch of the Star in Hours and Minutes; and the Use of it is to know the time of the Stars Rising and Setting, as also how long it continues above the Horizon.

First. For the Rising, take the Semi-Nocturnal Arch from the time of the Stars coming to the Meridian, and the Re∣mainder gives you the time of the Stars Rising. So the ☉ being in the beginning of ♊, the Spike of the Virgin comes to the Meridian at 9h. 18′ after Noon, from which take the Stars——5 11, Semi-Nocturnal Arch, there remains——4 07, which is the time of the Stars Rising in the Afternoon.

Secondly, For the Setting, add the Semi-Nocturnal Arch to the time of coming to the Meridian, and the Summe gives the time of the Stars Setting.

So on the same day, the ☉ being in the beginning of ♊, the Spike of the Virgin coming to the Meridian at 9h. 18′ if you •…•…dd to it the Star's Semi-nocturnal Arch, 5 11′ the Summe is 14h. 29′ past Noon, or 2h. 29′ past Mid∣night.

Thirdly, For the time of the Stars being above the Hori∣zon, double the Semi-Nocturnal Arch, and the Summe is the time of the Star's being above the Horizon.

The other Window sheweth the Star's Amplitude in Degrees and Minutes, which is counted from the East to∣wards the North, when the Star's Declination is North; and from the East to South, when the Declination is South: Where note, that the Stars Set at the same Distance from the West that they Rise from the East.

This Instrument was first invented by Mr. Samuel Foster, and given to me, drawn upon Pastboard by his own hand, which is still in my Power; but the Additions to it were put in by an Ingenious Gentleman of the French Nation, and by him drawn in Brass, which I received from him, and will keep for his Sake.

The following Table is made to insert all the Stars ex∣pressed there according to their Right Ascensions, which is fourfold as great as the true is, the Nature of the Instru∣ment requiring it to be so; because the Aequinoctial, which should be divided into twenty four hours, is divided but into six hours.

A Table

	A.	R.	As Rec. 4.	Decli.	Semi-Diur∣nal Arch.	Amplit.
	°	′					h.	mi.
Lucid. Comae Beren. ♎	182	45	731	00	30	06	8	48	53	30
Lucid. Lyrae ♑.	276	42	1106	48	38	32	24	00	00	00
Syrius. ♋.	98	00	392	00	16	15	4	33	26	43
Vindemiatrix. ♎.	191	53	767	32	•…•…2	35	7	05	〈◊〉〈◊〉	30
Spica Virginis. ♎.	197	23	789	32	9	33	5	11	15	27
Procyon. ♋.	110	57	443	48	6	00	6	30	9	40
Aquila. ♑.	294	06	1176	24	8	07	6	41	13	07
Luc. cap. Arieties. ♈.	27	38	110	32	22	03	8	04	37	05
Arcturus. ♏.	210	34	842	16	20	49	7	55	34	49
Cauda Delphin. ♒.	304	30	1218	00	10	14	6	54	16	35
Austra lanx ♎. ♏.	218	37	874	28	14	45	7	17	24	09
Cap. Medus. ♉.	42	15	169	00	39	47	12	00	00	00
Bo. lanx. ♎. ♏.	225	16	901	04	8	14	5	18	13	18
Luc. Hydr. ♌.	138	16	553	04	7	22	5	22	11	53
Luc. Pleiad. ♉.	52	26	209	44	23	10	8	11	39	12
Luc. Coron. Sep. ♏.	230	31	922	4	27	45	8	46	48	25
Os Pega. ♒,	322	28	1289	52	8	31	6	44	13	46
Med. nex. col. Serp: ♏	232	27	929	48	7	25	6	38	11	52
Bo. Fron. Scor. ♏.	237	02	948	08	18	57	4	18	31	27
Antares ♐. cor ♏.	242	50	971	20	25	42	3	30	44	00
Cor Leonis. ♌.	148	08	592	32	13	02	7	08	21	15
Luc. colli Leonis. ♌.	150	51	603	24	21	21	7	58	35	48
Luc. colli Peg. ♑.	336	30	1346	00	09	10	6	47	14	50
In basi Crater. ♍.	161	10	644	40	16	33	4	32	27	14
Marchab. Pega. ♓.	342	30	1370	00	13	37	7	11	22	13
Rigel. ♎.	75	07	300	28	8	33	5	16	13	49
Sin. Hum. Orion. ♊.	77	17	309	08	6	03	6	31	9	45
Cing. Orion. ♊.	80	18	321	12	1	24	5	54	2	15
Caput Ophiuci. ♐.	260	16	1041	04	12	49	7	06	20	52
Cauda Leonis. ♍.	173	28	693	52	16	13	7	26	26	39
Seq. Hum. Orion. ♊.	84	48	339	12	7	20	6	37	11	50
Cuspis Sagit. ♐.	266	00	1064	00	30	22	2	50	54	18
Cap. Andromed. ♓.	358	16	1433	04	27	28	8	44	47	48
Extrem. ala Pegas. ♓.	359	30	1438	00	13	32	7	10	22	05
Aldeban Tauri. ♊.	64	43	258	52	15	53	7	24	26	05

				The 5.	10	15	20	25
		°	′	°	′	°	′	°	′	°	′	°	′
♈	♎	00	00	18	20	36	44	55	12	73	48	92	36
♉	♏	111	36	130	48	150	16	170	04	190	08	210	32
♊	♐	231	12	252	08	273	24	294	52	316	28	338	12
♋	♑	360	00	381	48	403	32	425	08	446	36	467	48
♌	♒	488	48	509	28	529	52	549	56	569	44	589	12
♍	♓	608	24	627	24	646	12	664	48	6•…•…3	16	701	40

FINIS.