Report of Observations on the Transit of Mercury. 145 
luminous ring that shows, on the one side, the completion of the 
ingress, and on the other, the beginning of the egress, will de- 
pend not only upon the acuteness of the observer, but also upon 
the excellence of his instrument. The complete formation of 
the ring in the first internal contact, and its rupture in the second, 
furnish the best instants for observation. Professor Loomis de- 
termined the moment of the second internal contact. by taking 
the mean of three observations,—first, when a thin ring of 
light was seen between the limb of the planet and the sun; sec- 
ondly, when this ring was reduced to a bare line of light; and, 
thirdly, when there was a decided rupture of the ring. Thelow 
magnifying power of his telescope rendered this method expe- 
dient, although, had that power been great, the rupture of the 
ring might perhaps itself have afforded an instant sufficiently 
definite. 
The first internal contact, occurring as it did when the sun was 
near the meridian, and when the mind of the observer had had 
opportunity to gain entire composure, was probably the most fa- 
vorable instant of the whole for an accurate observation. Ac- 
cordingly, the discrepancies which the observations on this point 
present are within more moderate limits than those on the first 
external contact. Reducing to the longitude of New York, (no 
allowance being made for parallax, which would be a needless 
refinement in observations differing so much from each other, ) 
they are as follows: 
1st Internal Contact. 
h. m. 8. h. m. 8. 
New York, il’ 27 58:3 Cincinnati, IL 27 496 
Hudson,(Ohio,)11 27 15°6 West Point, 11 28 14-9 
Charleston, 11° 28 “36-4 
Least difference, 8-7s. Greatest difference, lm. 20°8s. 
The observations‘on the second internal contact present the 
following results: 
2nd. Internal Contact. 
Re: im 8. h. 8. 
New York, 5 50 55:7 Nantucket, 5 60 51:4 
Cincinnati, 5 50 480 West Point, 5 61 98 
Providence, 6 61 198 New Haven, 5 51 2146 
Charleston, 5 51 254 Washington, 5 62 460 
Vol. xx1x, No. 1.—April-June, 1845. 19 
