Royal Society. 129 



Greenwich since the erection of the new transit instrument, and as 

 computed by the solar tables of Delambre, which are used in the 

 computation of the Nautical Almanac, with a view to the discovery of 

 the errors in the elements of those tables. The result of the compa- 

 rison at first indicated the necessity of a correction of the epochs of the 

 sun's longitude, and of the longitude of the perigee, and perhaps also 

 of the equation of the centre. But upon pursuing the examination 

 through a series of years, it became manifest that some other source of 

 irregularity existed, and that this could be no other than an erroneous 

 estimate of the masses of some of the planets, especially of Venus 

 and of Mars. A more critical examination snowed that there was 

 also an error in the assigned mass of the moon. It was found necessary 

 in these investigations to take into account an error which occurred in 

 the tables with regard to the secular motion. It results from the au- 

 thor's researches that the epochs for 181 6, and those for 1821 to 1825, 

 ought to be increased respectively by 4",734 and 5",0(jl j that of the 

 perigee increased by 46",3, and the greatest equation of the centre 

 diminished by 0",84 j the mass of Venus should be reduced in the 

 proportion nearly of 9 to 8, and that of Mars nearly in the proportion 

 of 22 to 15. On a comparison of these results with those which have 

 been derived from an examination of some of Dr. Maskelyne's ob- 

 servations as given by Burckhardt in the Connaissance des Terns for 

 1816, they are found on the whole to agree in the most satisfactory 

 manner. 



Dec. 13. — A paper was read, entitled, " On the measurement of 

 high temperatures -, by James Prinsep, Esq., Assay Master of the 

 Mint at Benares, communicated by P. M. Roget, M.D. Sec. R.S." 



In the commencement of this paper the author describes the many 

 abortive endeavours of former experimenters to obtain instruments for 

 the accurate admeasurement of high temperatures, and afterwards 

 describes several attempts of his own to effect this very desirable ob- 

 ject. In the course of his inquiries a remarkable fact presented it- 

 self in the change which occurred in an index constructed on the 

 compensation-principle, and formed by two slips of meta^ the one 

 of silver, the other of gold, originally quite pure, and united without 

 any alloy. In the course of a few years, although it had never been 

 subjected to a very high temperature, the surface of the gold became 

 converted into an alloy of silver, the impregnation extending gra- 

 dually to a considerable depth in the gold, and destroying the sensibi- 

 lity of the instrument to changes of temperature. 



After trying various plans, he gave the preference to the one 

 founded on the following principles : namely, that the fusing points 

 of the pure metals are fixed and determinate ; that those of silver, 

 gold, and platina, comprehend a very extensive range of tempera- 

 ture ; and that between these three fixed points in the scale, as 

 many intermediate ones as may be required, may be obtained by 

 alloying the three metals together in different proportions. When 

 such a series of alloys has been once prepared, the heat of any 

 furnace may be expressed by the alloy of least fusibility which it is 

 capable of melting. The determinations afforded by a pyrometer 

 New Series. Vol. 3. No. U. Feb. 1828. S of 



