276 PHILOSOPHICAL TRANSACTIONS. [aNNO 1772. 



the basis of the sal catharticum amariim of the shops, or what goes by the name 

 of Epsom salts, otherwise it would have formed a salt easily soluble in water. 



IF^. yiccount of a Solar Eclipse observed at George's Island, by Captain fVallis, 

 and several Astronomical Observations made at Portsmouth. By Mr. George 

 Witchell, F. R. S., and Master of the Royal Academy at Portsmouth, p. 33. 



Extract of a Letter from Captain fFallis, June 20, 1771. 

 "Saturday, July 25th, 1767, being at anchor in his Majesty's ship Dolphin 

 in harbour, went on shore on a low point of land, not above 4 feet higher than 

 the sea, and observed an eclipse of the sun as below. Latitude, by the mean of 

 many observations, 17° 30' south, longitude, by various observations of the 

 distance of the sun from the moon, between 149° 30' and 149° 50' west from 

 London. The eclipse began at 6^ SI'" 50' ap. t, and ended at 8*^ l'"0'; 

 duration 1** 9™ 10*. They were not certain of the instant of the beginning of 

 the eclipse, from a little negligence; but very certain of the end." 



Remarks by Mr. W. — As the sun's altitudes are given, without any correction, 

 Mr. W. supposes they were taken by bringing down the image of the sun, till 

 it appeared bisected by the visible horizon: he therefore recomputed the time, by 

 allowing for the dip and refraction, which together amount to 8*". This correc- 

 tion makes the apparent time of the beginning 6*" 51"" 12% and the end 

 gh Qta 37s. hence the duration of the eclipse was l*" 9" 25*; but, by a careful 

 computation from Mayer's new tables, the duration should have been 1^13™ 204-% 

 which is almost 4*" longer than the observation affords; but as it is remarked 

 that the beginning was not exactly taken, and the moon entering very obliquely on 

 the sun, the defect in 4"* would be but little. It seems most reasonable to 

 attribute the whole of the error to the beginning of the eclipse. Mr. W. there- 

 fore deduced the longitude from the end, and made it to be g^ 55™ 55' west from 

 Greenwich, or 148° 58'-f, which is 4l'4^ less than the mean result of the lunar 

 observations, which, considering all circumstances, is not a very great difference for 

 the first observations that were ever made on this island. 



Astronomical Observations made at the Royal Academy, Portsmouth. 



1769, May 9, ate'' 13™ 9% apparent time, Mr. Bradley observed the immer- 

 sion of ^ n°""" by the moon ; uncertain to a few minutes, on account of the 

 strong twilight. The emersion was not taken. The transit of Venus, 

 and solar eclipse, next morning, were both observed here; but, having then no 

 better instrument for determining the going of the clock, than an indifferent 

 Hadley's sextant, I do not think the observations worthy of being laid before the 

 society; and, for the same reason, omit the observations of the comet. 



1770, April 7, at ll** 23™ 33', ap. time, by Mr. Bradley's observation, the 



