292 TRANSACTIONS OF THE SOCIETY OF 



discharge, which does not exist in the electric battery. The explanation of this 

 singular fact is found in the difference of accumulation and tension of the elec- 

 tricity at the two extremities of the inductive wire, and in the elevation of tem- 

 perature of which the negative pole is the seat. 



M. Wartmann also communicated (November 16, 1865) some observations 

 which he had made on the appearance, of the sjjark produced in a vacuum by 

 currents of induction. This spark is elongated ; at the positive pole it some- 

 times presents a reddish effluence, and at the negative pole it becomes violet. 

 By employing for the electrode a cylinder of soft iron, the reddish effluence was 

 environed by a violet aureole. With reference to these researches, he an- 

 nounced (December 7, 1865,) that he had made use of a tube of glass, having 

 two concentric chambers without communication with one another, and each 

 enclosing traces of a gas different from the gas of the other. The positive 

 electrode was in one of the chambers, the negative in the other. When, in this 

 case, a powerful coil is employed, the course of the current may be reversed 

 without changing the colored appearance at the two poles. M. Wartmann states 

 that, contrary to what is affirmed by the manufaetvirers of the tubes of Geissler, 

 he has found that in process of time the tubes, so far from improving, lose some- 

 thing of their efficacy. He remarked also that after new researches he has 

 seen no influence exerted by magnetism on the stripes of the spectrum, which is 

 a confirmation of the conclusions he had advanced several years before. 



Professor Volpicelli, honorary member of the society, ( present at the meeting 

 of September 7, 1865,) took occasion to observe that, although we have nu- 

 merous investigations respecting the quantity of atmospheric electricity, the 

 nature of that electricity has been little studied. He thinks that he has observed 

 a diurnal qualitative period in the atmospheric electricity, a quotidian passage 

 from positive to negative. He is of opinion that for this kind of researches it 

 is necessary to return to the method of Franklin. 



Professor Marignac, in reference to the researches published in France on 

 aeronautics by wmgs, maintains (October 5, 1865) that their authors have 

 proceeded on entirely false data as regards the quantity of labor necessary in 

 order that a machine for flying should sustain itself in the air. According to 

 his calculations, in a machine of this sort, the ratio of the motive force to the 

 weight raised varies as the square root of the section of the wings. The motive 

 force should augment proportionally to the square of the weight raised, which is 

 an unfavorable condition for the realization of such machines. From this it 

 would result that, if all birds had the same form and structure, the largest 

 would fly with least facility. 



M. Cellerier presented (November 2, 1865) a memoir on the measurement of 

 gravity by means of the inversion pendulurh of BesseL He showed that, for 

 this kind of observations, it is requisite to attain a relative exactness of at least 

 one hundred-thousandth. Setting aside the errors pertaining to the measures of 

 time, there are others which are found to act on the inversion pendulum, so that 

 the alteration which results therefrom in the duration of the oscillations, accord- 

 ing to the two suspensions necessary to this apparatus, is constantly in the same 

 ratio, and the alteration which results in the two cases, from the defect of the 

 measurement of distance of the points of suspension, is also in the same ratio 

 By means of the two observations of duration, it is thus practicable to eliminate 

 at once all these small alterations, and to obtain the duration reduced to a vac- 

 uum. This result is oi great importance, because the accidental movements of 

 the air have never been susceptible of being exactly appreciated. The apparatus 

 of Bessel may thus lead to a rectification of the value assigned to gravitation. 



General Dufour (December 21, 1865) gave details of the direct levelling now 

 in process of execution in Switzerland. The plate fixed in the stone of the 

 Niton at Geneva will serve as the point of reference ; and of course there will 

 be negative numbers, as BS,le is nearly 200 metres lower. Professor Planta- 



