284 Dr. II . Her wig's Investigations on the Conformity 



stinct, and that the light of the sun during an eclipse should be 

 increased rather than diminished. Again, we should expect 

 that such variations would be produced by changes of tempera- 

 ture that they could scarcely fail to be detected. 



We then conclude that the polariscope gives only negative re- 

 sults, and cannot be regarded as proving that the light is reflected. 

 The evidence of the spectroscope needs confirmation, since the 

 dark lines may have been invisible owing to the feeble light of 

 the corona. But if the observations with it are correct, the self- 

 luminous character of the corona is established. The thermo- 

 metric and actinic experiments point towards a lunar atmosphere 

 as the cause of the corona. 



In the above I have endeavoured to give the evidence in favour 

 of each view, unbiased by any theory, leaving to those best able 

 to judge to determine whether either explains all the facts ob- 

 served. The absence of a lunar atmosphere is so generally ad- 

 mitted, that its existence is suggested only with reluctance, and 

 merely as the most natural explanation of the observations. 



Boston, U.S., Sept. 1, 1869. 



XXXIV. Investigations on the Conformity of Vapours to Mariotte 



and Gay-Lussac's Law. By Dr. Hermann Herwig*. 



[With a Plate.] 



§1. 



THE relation which, according to the twofold law of Mariotte 

 and Gay-Lussac, in the case of an elastic fluid connects 

 the three quantities the pressure P, the volume V, and the ab- 

 solute temperature a + t, cannot, after the experiments of Reg- 

 nault, be considered strictly valid for permanent gases. Many 

 important deviations from this law may be acounted for by the 

 vapours being near their point of condensation. Very few direct 

 experiments have been made as to the actual relation holding in 

 the case of vapours between the quantities P, V, and (« + /). 

 More frequently has half this problem been attacked, by assuming 

 the constancy of one of these three quantities and deducing the 

 reciprocal dependence of the other two. 



The first more nearly exact numbers were given almost simul- 

 taneously by Bineau and Cahours. Bineau f found the vapour- 

 densities of acetic acid, of formic acid, and of sulphuric acid too high; 

 whereupon Cahours pointed out the influence of the selection 

 of too low temperatures by Bineau ; for he showed for several 

 bodies under a constant pressure (of one atmosphere) the mutual 



* Communicated by the Author, having been read before the Nieder- 

 rheinische Gesellschaft fur Natur- und Heilkunde, August and November 

 1868. Translated by H. R. Greer, Esq., B.A. 



-\- Comptes Rendus, vol. xix. p. 7^7. 



