VOL. LVI.] PHILOSOPHICAL TRANSACTIONS. 287 



that it seems impossible to obtain the least light from them. Perhaps we may 

 hereafter receive from some southern parts, observations sufficient to make out 

 the true orbit of this comet. 



X. Account of a Comet seen by Mr. Alexander Brice, dated Kirknewton, 



April 11, 1766. p. 66. 

 This comet Mr. B. observed, April 9 and 10, in the north-west, and very 

 near the horizon. It began to appear at half an hour after 8 o'clock, and set 

 2?} minutes after Q. The tail was very visible to the naked eye; but the nucleus 

 could not be seen without a telescope, through which it appeared very distinctly, 

 like a star of the 4th or 5th magnitude. It was surrounded with a gleam of 

 light, hke what is seen round the stars in Orion's sword, commonly called 

 Janua Coeli. The tail stretched upwards, and inclined to the west, and was 

 about 4 degrees long: the body of the comet was also 4 degrees distant from the 

 new moon (then 34 hours after the change) and almost perpendicular above it; 

 and it appeared to more advantage after the moon was set. The comet, when 

 setting, was 37° to the north of due west, and 13° more northerly than the 

 Pleiades, below them, but in the same tract: it was descending towards the sun, 

 at the rate of 6°, as near as he could guess, in the space of 24 hours. 



XI. A Report concerning the Microscope-Glasses, sent as a Present to the Royal 



Society,* by Father di Torre of Naples, and referred to the Examination of 



Mr. Baker, F. R. S. p. 67. 



These microscopes are globules of glass, formed over a lamp, by Father di 

 Torre, and ingeniously placed in cells of brass, adapted to Wilson's microscope. 

 Four of these cells, thus furnished, were sent as a present from the Father to 

 this Society, under the care of our late worthy member Sir Francis Eyies Stiles: 

 but when they came into Mr. Baker's hands, one of these minute glasses was 

 wanting, having probably been shaken out of its cell in carriage: the loss, 

 however, signifies little, as there remains another of the same magnifying power. 

 These globules are wonderfully small : the largest being in diameter only 1 Paris 

 points, and said to magnify the diameter of an object 640 times; the second is the 

 size of one Paris point, magnifying thediameterof an object 1 280 times; and the third 

 is so extremely minute, as to be no more than one half of a Paris point, or the 144 th 

 part of an inch in diameter, and is said to magnify the diameter of an object 256o 

 times, and consequently it must magnify thesquareof such diameter 6,553,600 times. 



Now as the focus of a glass globule is at the distance of -J^th of its diameter, it 

 is with the utmost difficulty that globules so minute as these can be employed to 

 any purpose. For instance, the focus of that globule, whose diameter is but 

 one half of a Paris point (or the 144th part of an inch) is no farther from the 

 object to be examined, than the 576th part of an inch. In attempting to find 



* Vid. p. 245 of this vol. 



