Page:Philosophical Transactions - Volume 004.djvu/57

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	H.	m.	sec.		H.	m.	sec.
E. g. Suppose March 11th in the Morning, when, the Sun half appears above the Horizon, the Watch points at	5	30	10		0	10	3
In the Evening, when the Sun appears half set, ay	5	20	6		11	59	57
To know by the Watch the time elaps'd between both, subduct the time of the rising	5	30	10
From	12	0	0
Rests	6	29	50
Whereunto adding the time of the setting	5	20	6
There comes for the time elapsed between them	11	49	56		11	49	56
Whereof the half is	5	54	58		5	54	58
Which added to the time of the Suns rising	5	30	10		0	10	3
There comes the time of the Watch when the Sun was in the South	11	25	8	diff.	6	5	1
To which adding the Æquation of the 11th of March	0	7	45		0	7	45
The Summe is	11	32	53		6	12	46
Seven days after, viz. March 18, let the rising of the Sun be observ'd, and the Watch point then at	5	19	4		11	58	57
And at his setting, let the Watch point at	5	25	2		0	4	55
To find the time elaps'd between them, subduct the time of the rising.	5	19	4	Or,	11	58	51
From	12	0	0		24	0	0
Rests	6	40	56		12	1	3
To which adde the time of the setting	5	25	2		0	4	55
And you'l find the time past between them	12	5	58		12	5	58
Whereof the half is	6	2	59		6	2	59
Which adde to the time of the rising	5	19	4		11	58	57
And you have the time when the Sun was in the South	11	22	3		6	1	56
Whereunto adding the Æquation of March 18	0	10	1		0	10	1
The Summe is	11	32	4		6	11	57
Which Summe if it had agreed with the first, viz.	11	32	53		6	12	46

then, had the watch been set to the right measure; but seeing the latter is less than the former, the difference being 49. sec; the Watch hath by so much, in 7. days, gone too slow;; which 49 Sec. divided by the number of days, you have 7 Sec. for the daily difference; and by so much the Watch goes too slow in 24. hours.

You may also, instead of the Suns rising and setting, take two equall Altitudes of the Sun, before and after Noon, and having noted the time given by the Watches at the time of both the Observations, proceed with it in the same manner, as was Iust now directed for observing the Sun in the Horizon. In either of which ways there may be some Error, caused by