M. de Sauffure's Tjiaphanometcr. 377 



an ink of a red colour, like that of the rofa ceni'ifolia, which 

 again disappeared when the paper became cold. I was not 

 able to obtain it of a darker tint; but I muft confefs that I 

 made only a few experiments for that purpofe, as I was 

 fat'isiied with the colour I had got. 



VII. Defcrlpliori of M. de Saussure's Diapbanometer*. 

 By Dr. F. W. Aug. Murhard, of Gottingen. From 

 Neuefi Journal der Phyfik, by ProfefJ^r Gren. Vol. IK 



J. HIS inftrumeni, firft defcribed by M. de Sauflure in 

 the fourth volume of the Memoirs of the Royal Academy of 

 Sciences at Turin, lias fome refemblance to the cyanovicter * f 

 both in regard to its object and conftruction. The principal 

 difference is, that the latter (hews the whole effeit of the va- 

 pour and evaporation diffufed throughout the atmofphere, 

 from the eye of the obferver to the utmoft boundary of his 

 view ; while the diaphanomctcr is, on the other hand, de- 

 ficmed to fliew the greatnefs of the evaporations exifting in 

 any limited part of the atmofphcre which furrounds us. 



The meafure of tranfparency in M. de Sauffure's inftru- 

 ment, is founded on the proportion of the diftances at which 

 determined objects ccafe to be vifible; and the point was to 

 find objects, the difappearance of which, at a certain diftance, 

 could be determined with the greateft accuracy. M. de 

 Sauflure found that the moment of difappearance can be ob- 

 served much more accurately when a black object is placed 

 on a white ground, than when a white object is placed on a 

 black ground ; that the accuracy was ftill greater when the 

 obfervation was made in the fun, than in the (hade; and 

 that even a ftill greater degree of accuracy was obtained, 

 when the white fpace furrounding a black circle, was itlclf 

 furrounded by a circle or ground of a dark colour. This laft 



An iuftrumetu for determining the degree of the bluenefs of the 



he a' 



circumftauco 



