VOI« LX.] PHILOSOPHICAL TRANSACTIONS. 31 



about B.S.E., and extends itself through the zenith, and vanishes near the hori- 

 zon, about thew. N. w. It has very seldom any motion at all; and when it 

 has, it is only a small tremulous one on the two borders. On the 7 th of August 

 thev took their departure from the Factory, and sailed on their return home- 

 wards. The latitude of the factory Mr. W. makes 58° 55'4-. 



The prodigious difference between the latitude of Churchill factory, as laid down 

 from observations made by Hadley's quadrant, and that deduced from the observa- 

 tions made with the astronomical quadrant on shore, has often employed Mr. W.'s 

 most serious attention ; but he cannot think on any probable cause for such dif- 

 ference, unless it lie in the very great refractive power of the air in- these parts. 

 He has mentioned how the ice and land appear to be lifted up, when persons 

 stand on the ship's deck: and if the visible horizon be lifted up in like manner, 

 it must make its apparent distance from the sun, or, which is the same thing, 

 the sun's apparent altitude, less than it otherwise would be; and consequently, 

 the latitude greater than the truth ; and also greater than it will be shown by a 

 land quadrant, which depends not on the horizon, agreeable to what is found ia 

 the case before us.* 



Before quitting this part of the world, Mr. W. observed that he had abundant 

 reason, in his voyage home through Hudson's Straits, and the adjacent seas, to 

 rest satisfied with having ventured his opinion in respect to the quick motion, or 

 swift dissolution, of the ice islands. For after they left the Straits they had not 

 seen one ; and though they were becalmed, and much troubled with contrary 

 winds, so that they lay beating from side to side about 9 days in the Straits, yet 

 they did not see 20 islands the whole time, and these none of them very large. 

 Whereas, was Capt. Middleton's hypothesis true, and they were some hundreds 

 of years dissolving, and travelling into the latitude of 50°, they could not have 

 got by this time quite out of Hudson's Straits, much less out of the Straits of 

 Davis. 



Oct. 11, at noon, the Lizard light-houses bore n. e. by n. dist. by estimation 



* Having mentioned this circumstance to the Rev. Mr. Maskelyne, it immediately occurred to 

 him, that the longitude deduced from observations of the D 's distance from the sun or a star, would 

 be considerably affected by this cause, a.s not only the altitudes of the Q , from whence the time at 

 the ship is found; but also the latitude of the ship, found by an observation of the sun's meridional 

 altitude, or otherwise, will cotispire to increase the sun's distance from the meridian, or angle at the 

 pole. Mr. W. therefore recomputed the longitude from his observation of the moon's distance from 

 the sun, taken August 5th, 1768, on a supposition that the mean error in any altitude taken by 

 Hadley's quadrant, arising from this cause, is 10 minutes j and found that on such a supposition, 

 which it must be allowed appears to be extremely well founded, the longitude will be 11 'J less than 

 what he found it at the time when he made the observation, and therefore the longitude of Churchill 

 will in this case be only 94" oO'§ w. And by making a similar correction of 15' to Mr. .Dymond'd 

 observation of the 6th, it will give the longitude of Churchill 95" 18' w.-rOrig. 



