Notices respectingNew Books. 133 



or was at its greatest altitude, or burst, or disappeared, and again 

 when they hear the souud ; and, as common watches are lliable 

 to vary much in a few hours, that they would, as soon after as 

 may be, find the error of their watch by comparing it with a good 

 regulator ; for, if the exact times could be Iiad at different places, 

 the absolute velocity of the meteor, the velocity of the sound 

 propagated to us from the higher regions of the atmosphere, and 

 the longitudes of places might be determined. 



Even in cloudy weather it might be useful to note the times of 

 accidental explosions, or any unusual sounds heard, with the 

 points of the compass from which they are thought to come, 

 whether in tlie day or night, and of sudden illuminations of the 

 sky in the night, as they may prove afterwards to have been 

 owing to meteors, rjid will serve some of the pur])oses above 

 mentioned. 



Th.ese meteors generally leave a visible tract of faint light be- 

 hind them, which gives time to observers to ascertain the path, 

 either by the stars near it, or the observations of altitudes and 

 bearings. Meteors are sometimes seen in the day-light. 



It may not be a;niss to apprize ol)servers, that estimations of 

 altitudes made without an instrument are very uncertain, owing 

 to the apparent figure of the sky being the segment of a sphere, 

 whose centre is greatly below the surface of the earth ; so that 

 persons will be apt to judge an object which is near the horizon 

 to be much higher than it is; at 2.i" of altitude, they may think it 

 at 45°; and to be in or near the zenith, when with an instrument 

 it would be found 10 or 20 degrees from it. This points out the 

 necessity for observers to mention, whether they estimated their 

 altitudes, or observed them with an instrument. 

 Greenwich, Nov. fi, 1783. N. M. 



XXV. Notices respecting New Books. 



A Voyage to SpitzherQen, containing an Account of that 

 Country, of the Zoology of the North, of the Shetland Isles, 

 and of tlic IVhale Fishery. By John Laing, Surgeon. 2d 

 Edition, r2mo, corrected and enlarged, pp. 165. 



IN the little volnme before us, we have an interesting addition 

 made to the natural history of regions of which our knowledge 

 is as yet, comparatively speaking, but imperfect. Mr. Laing 

 has been evidently a diligent and acute observer, and communi- 

 cates the fruits of his observation in a simple and perspicuous 

 manner. The description which we subjoin of the Phocce class 

 of amphibious animals, all the accounts hitherto given of which 

 by voyagers and naturalists are extremely confused, may betaken 

 as a favourable specimen of the work. 



13 " Tlie 



