45(3 PHILOSOPHICAL TRANSACTIONS. [ANNO 1783. 



rather complex. From the experiments and trials made with it, Mr. C. con- 

 cludes, that when it is in good order, it exhausts the air about 1000 times. 



XXI V. Observation of the Transit of Mercury over the Sun, of Nov. 12, 

 1782, observed at Cook's Town, near Dungannon, in Ireland. By the Rev. 

 James Augustus Hamilton, M.A. p. 453. 



After some introductory lines, Mr. H. proceeds, I observed with an achro- 

 matic tube of 3 inches aperture, triple object-glass, and used a magnifying 

 power of about 90 times, which I preferred on account of the state of the at- 

 mosphere. At about 2 o'clock. I set a stop watch to apparent solar time, and 

 placed myself at the telescope within hearing of the beat of the transit-clock. 

 I kept the part of the disc where I expected the ingress in constant view, my 

 sight being directed by a vertical wire in the eye-tube, and at 2 h 22 m 3 s I stopped 

 the watch, and counted 20 s , to be sure of my having really perceived the first 

 impression (which I apprehend could not have been shown I s sooner by the 

 power, &c. I used.) I then stopped seconds to the clock, and counted up to an 

 even minute, and found, that the first external contact happened at 17 h 33 m 11 s 

 by the clock, or 2 1 ' 21 m 45 s apparent time. Mercury came in like a distinct 

 black point, without any preceding haziness or appearance of atmosphere; and 

 at I7 h 39 m 10 s by the clock, or 2 h 27 m 43 s apparent time, the thread of light 

 seemed compleated, and then I date the internal contact. I had no instrument 

 fit to take any micrometer measures, so continued only looking at the planet till 

 the sun got so low, that the limb presented the appearance of a troubled sea at 

 a distant horizon, among the waves of which Mercury once more plunged at 

 about 18 h 52 m , and the sun and planet both left my view at about 18 h 57 m ; but 

 these observations are only good conjectures. From my best observations of 

 eclipses of Jupiter's first satellite, of appulses of the moon's centre to the meri- 

 dians, and lunar distances with a Hadley's quadrant, I make my longitude 

 26 m 35 s w. nearly, and my latitude by a mean of many observations, is 

 54° 38' 20". 



XXV. Method of finding Curve Lines from the Property of the Variations of 

 Curvature. By Nicholas Landerbech, Adjunct Mathematical Professor at 

 Upsal. p. 456. 



Thesubject of this paper may be found treated in several of our books on fluxions. 



XXVI. A Series of Observations on, and a Discovery of, the Period of the Va- 

 riation of the Light of the bright Star in the Head of Medusa, called Algol. 

 By John Goodricke, Esq. Dated York, May 12, 1783. p. 474. 



The following observations, lately made, exhibit a regular and periodical varia- 



