220 Intelligence and Miscellaneous Articles. 



intend to undertake a further course of experiments in order to 

 obtain an accurate determination, the purpose of the present paper 

 being merely to show the method. — Proceedings of the American 

 Academy of Arts and Sciences, May 26, 1885. 



NEW FORM OF HYGROMETER. BY M. BOURBOUZE. 



When vapour begins to condense on a glass plate interposed 

 between the observer and the source of light, concentric rings begin 

 to appear at this point. They are like those seen round the cloud 

 in foggy weather. 



The apparatus we have constructed to produce these rings con- 

 sists of a small rectangular tube, with small holes on opposite faces 

 closed by very thin glass plates. A very delicate thermometer is 

 placed so as to dip in only a small quantity of the liquid. When 

 a current of air is produced in the liquid either by blowing or by 

 aspirating, a deposit of dew rapidly forms on the glass. If the 

 apparatus is placed between the eye and a point of light, concentric 

 rings are seen about this point, red outside and violet within. The 

 appearance of the rings as well as the reading of the thermometer 

 may be made from a distance by a telescope. — Gomptes Rendus, 

 June 22, 1885. 



ON THE DISENGAGEMENT OF HEAT IN THE SWELLING AND 

 SOLUTION OF COLLOIDS. BY E. WIEDEMANN AND CH. 



LUDEKING. 



The conclusions of this research are as follows : — 



The solution of the dry colloid is made up of two processes : — 



(1) hydration, which is attended with disengagement of heat; 



and (2) solution, which is attended with absorption of heat. — 



Wiedemann's Annalen, No. 6, 1885. 



ON A MERCURY-GALVANOMETER. BY G. LIPPMANN. 



A mercury-manometer is placed between the poles of a fixed 

 magnet, which lie right and left of its horizontal arm. The current 

 traverses the latter in a vertical direction parallel to the axis of the 

 tube, by which the mercury rises in one limb. 



If i is the strength of the current, H the strength of the mag- 

 netic field, I the length of a small rectangular parallel opipedon in 

 the direction of the current, e its thickness in the direction of the 

 lines of force, the force which displaces the parallelopipedon is Hit, 



j i.i_ HZi Hi 



and the pressure ^>=— - = — 



Hence the sensitiveness increases with the strength of the mag- 

 netic field and the thinness of the column of mercury. Accordingly 

 the lower bend of the manometer is replaced by a chamber filled 

 with mercury at right angles to the current, and only -^ millim. in 

 thickness.— Comptes Rendus, 1884, pp. 1256-57 ; BeibVdtter der 

 Physik, No. 6, 1885. 



