PHYSICS AND NATURAL HISTORY, OF GENEVA. 203 



solution of iodine in tlic snlphuret of cnibon ; this substance completely obstructs 

 the passage of the light witliont intercepting the heat. The interesting investi- 

 gations of M. Tyndall on the invisible rays of the electric light and on the 

 calorescence were also analyzed by JVI. Soret. 



Professor Wartmann made a report on tlie observations of M. Oastracane, 

 and on the employment of monochromatic light applied to the microscope. M. 

 Castracane has availed himself of this process in his researches on living and 

 fossil diatomeaj, of which he will soon publish an atlas, and M. Wartmann ex- 

 hibited to the society photographic images of these minute organisms which the 

 learned Italian has succeeded in obtaining. M. Wartmann also presented a 

 report on the memoir of M. Plateau relative to a curious problem of magnetism, 

 the possibility, namely, of maintaining a magnetic body in stable equilibrium by 

 magnetic forces. The same problem was made the subject of remarks offered 

 by MM. Lucicn de la Rive and Cellerier. The latter examined particularly 

 the case in which the force, instead of acting in the inverse ratio of the square 

 of the distance, would act in the inverse ratio of the fifth power, as this occurs 

 with bodies electriiied by induction, and he proved that neither in this case 

 could a stable equilibrium be obtained. 



Professor Marignac communicated the first results of a series of researches 

 which he has undertaken on the niobium. {Bib. U/iivers., Archives, Sec, vol. 

 xxiii.) He first examined the double fluorides which the hypouiobic fluoride 

 forms with other metallic fluorides, and has arrived at the conclusion that the 

 byponiobium is not an allotropic modification of niobium, but rather an oxide of 

 niobium. He has also recognized the association of tantalic acid with hyponio- 

 bic acid in the colombitcs of America, and he indicates a means of separating 

 them. He proves, finally, that tantalic acid comprises five equivalents of oxy- 

 gen, like the hyponiobic acid. Professor Marignac also read a note {B/b. Uni- 

 vers., Arc/fires, &c., vol. jixii) on certain consequences which result from the re- 

 searches of M. Karl Than, relative to the anomalous density of the vapor of sal 

 ammoniac, and from those of M. Deville on the decomposition of water by heat. 

 M. Marignac pointed out that the combination of two bodies frequently gives 

 rise to a temperature much more elevated than that which is necessary in order 

 to effect the decomposition of the compounds which they form. It results from 

 this, that the time requisite for the accomplishment of a combination or a com- 

 bustion depends on the rapidity with which the surplus of heat produced by 

 that act is capable of being dissipated by communicating itself to the surround- 

 ing bodies ; this interval might even become very long, if the question related 

 to bodies forming a considerable mass entirely isolated in space, and unable to 

 part with heat except by the slow process of radiation. 



M, Delafontaiue read to the society a memoir, in Avhich he i-ecites a first se- 

 ries of researches on the earths of the gadolinite ; his experiments related to 

 erbiue, terbine, and yttria, of which oxides he has determined the atomic weight 

 by analyses of their sulphates, and he combats the opinion pronounced by M. 

 Popp, that erbine is one of the oxides of cerite. The same member presented 

 a series of researches on the salts of molybdic acid, {Bib. Univers., Archives, &c., 

 vol. xxiii,) and on their comparison with the tungstates ; he has detected two 

 series of salts : one of which is composed of neutral salts, and the other is par- 

 allel to the paratungstates. Pie exhibited to the society a fragment of meteo- 

 rite, picked up after the fall of a large number of aerolites, which occurred May 

 14, 1864, in the environs of Montauban. The matter composing this fragment 

 is of a porous appearance and a relatively slight density ; it contains 13 per cent, 

 of Avater, and 6 per cent, of a substance very simdar to lignite. Another memoir 

 which M. Delafontaiue read to the society relates to his researches on the spectra 

 of absorption, {Bib. Univers., Archives, &c., vol. xxii) ; when the rays of the 

 solar spectrum are made to pass through a solution of certain metals, we obtain 

 a spectrum much modified ; certain bands more or less large may then be ob- 



