316 Lit ell "ujc nee and Miscellaneous Articles. 



trary case, rays of the same wave-length, taken from different 

 spectra, may have notably different properties. 



We can, however, already state that, the intensity being the 

 same in the red for the four spectra, the weakening towards the 

 violet varies with eacli source, according to a certain fuuetion of 

 the temperature ; and without being able yet to attempt a measure- 

 ment of this, we can already arrange them in the order of increasing 

 temperatures : — moderator lamp ; steariue candle ; illuminating- 

 gas, of which I have not given the less -accordant Tables ; Drum- 

 in ond light ; electric light, and, lastly, the solar light, which cor- 

 responds to an emission-temperature much higher than that of the 

 electric light, in spite of the uncertainty caused by the absorptions 

 it has undergoue from its transmission through the gaseous en- 

 velopes of the sun and our atmosphere. 



It will be possible to make rigorously exact measurement of the 

 temperatures in the spectrometric way as soon as we know the 

 precise law of emission for all the radiations and the numerical 

 constants for each wave-length. The results contained in this Note 

 may be regarded as a first essay towards the solution of this im- 

 portant question. — Comptes Bendus de V Academic des /Sciences, 

 August 19, 1878, tome lxxxvii. pp. 322-325. 



ON THE EXCITATION OF ELECTRICITY BY PRESSURE AND 

 FRICTION. BY H. FRITSCH, OF KONIGSBERG, PRUSSIA. 



1. It is well known that many crystalline bodies can be power- 

 fully electrified by pressure. This, however, takes place in each 

 case only under a perfectly definite condition. Calc-spar becomes 

 electric only when pressed against another substance, never when 

 pressed against another piece of calc-spar. Three pieces of calc- 

 spar were laid one upon another ; a pressure was then exerted upon 

 the uppermost, which would have made each of the pieces singly di- 

 stinctly electric : the central piece proved to be quite devoid of 

 excitation ; only the two outer ones possessed the usual quantity 

 of electricity. If two calc-spars were pressed against one another, 

 the surfaces which were in contact with the foreign bodies by 

 which the pressure was exerted exhibited electricity distinctly ; the 

 two inner surfaces, where calc-spar had been in contact with calc- 

 spar, were without excitation. I have not yet succeeded in carry- 

 ing out the same experiment with other bodies. 



2. According to previous observations, a definite substance, on 

 undergoing friction against another, acquires always a certain in- 

 variable electrical excitation independent of the collateral circum- 

 stances, and accordingly the nature of the electricity excited is 

 constantly the same. To test the correctness of this position the 

 following experiments were instituted, in which the collateral 

 circumstances were varied as much as possible. 



n. With a violin-bow I stroked plates of zinc, copper, brass, and 



