278 PHILOSOPHICAL TRANSACTIONS. [ANNO 1798. 



We may avail ourselves of the observations that relate to the distances at which 

 the satellites vanish, to determine their relative brightness. The 2d satellite ap- 

 pears generally brighter than the 1 st ; but, as the former is usually lost farther from 

 the planet than the latter, we may admit the 1st satellite to be rather brighter than 

 the 2d. This seems to be confirmed by the observation of March 9, 1791 ; where 

 the 2d appeared to be smaller than the 1 st, though the latter was only 25" from the 

 planet, while the other was 30".8. The first of the new satellites will hardly ever 

 be seen otherwise than about its greatest elongations, but cannot be much inferior 

 in brightness to the other 2 ; and if any more interior satellites should exist, we 

 shall probably not obtain a sight of them ; for the same reason that the inhabitants 

 of the Georgian planet perhaps never can discover the existence of our earth, 

 Venus, and Mercury. The 2d new or intermediate satellite is considerably smaller 

 than the 1st and 2d old satellites. The 2 exterior, or 5th and 6th satellites, are the 

 smallest of all, and must chiefly be looked for in their greatest elongations. 



Periodical revolutions of the new satellites. — It may be some satisfaction to know 

 what time the 4 additional satellites probably employ in revolving round the planet. 

 Now, as this can only be ascertained with accuracy by many observations, we must 

 of course remain in suspense till a series of them can be properly instituted. But, 

 in the mean time, we may admit the distance of the interior satellite to be 25 // .5, 

 as our calculation of the estimation of March 5, 1794, gives it ; and from this we 

 compute that its periodical revolution will be 5 days, 21 hours, 25 minutes. — If we 

 place the intermediate satellite at an equal distance between the 2 old ones, or at 

 38".57, its period will be 10 days, 23 hours, 4 minutes. — By the figure of Feb. 9, 

 1790, it seems that the nearest exterior satellite is about double the distance of the 

 farthest old one ; hence its periodical time is found to be 38 days, 1 hour, 49 mi- 

 nutes. — The most distant satellite, -according to the calculation of the observation 

 of Feb. 28, 1794, is full 4 times as far from the planet as the old 2d satellite ; it 

 will therefore take at least 107 days, 16 hours, 40 minutes, to complete one revo- 

 lution. — It will hardly be necessary to add, that the accuracy of these periods de- 

 pends entirely on the truth of the assumed distances ; some considerable difference 

 therefore may be expected, when observations shall furnish us with proper data for 

 more accurate determinations. 



IV. An Inquiry concerning the Source of the Heat which is excited by Friction. By 

 Bervjamin Count of Rumford, F. R. S. } M. R. I. A. p. 80. 



Being engaged lately in superintending the boring of cannon in the workshops 

 of the military arsenal at Munich, I was struck with the very considerable degree 

 of heat which a brass gun acquires, in a short time, in being bored ; and with the 

 still more intense heat, much greater than that of boiling water, as I found by 

 experiment, of the metallic chips separated from it by the borer. From whence 

 comes the heat actually produced in the mechanical operation above-mentioned ? 

 Is it furnished by the metallic chips which are separated by the borer from the solid 



