B. TERRESTRIAL PHYSICS AND METEOROLOGY. 119 



phenomena occurring in the winter and spring months. They 

 take place on calm clays, and their duration is very limited, 

 and no instance is on record of any appearance of a circular 

 motion of the clouds. 12 A, X., 65. 



A SENSITIVE VARIATION BAROMETER. 



Kohlrausch, in describing an ingenious barometer devised 

 by him, very correctly remarks that such an instrument, 

 which combines with unbounded sensitiveness the absence of 

 any friction, which requires only a single observation to be 

 made, which consumes no time, and possesses so slight a mo- 

 ment of inertia that it follows the variation of the atmos- 

 pheric pressure in the fraction of a second, would probably 

 excite some interest. The instrument devised by him con- 

 sists of a metallic ring, such as belongs to a Bourdon aneroid, 

 one side of which is firmly screwed to a holder. The other 

 free end pushes against a small mirror in a metal frame, 

 which is suspended on little springs of pendulum steel. A 

 scale is placed about ten feet distant from the mirror, so that 

 two inches of ordinary barometric change correspond to three 

 feet on the scale. The influence of temperature upon the ap- 

 paratus is extremely great, but, by introducing a proper 

 amount of air within the tube, this may be reduced to a 

 very small quantity. A curve is given showing the course 

 of barometric pressure during three minutes of time on the 

 occasion of a very stormy day, observations being noted 

 down every three seconds. Kohlrausch states that he has 

 never been able to detect any connection between baromet- 

 ric oscillations and flashes of lightning. 7 A, 18^4, XL VII., 

 362. 



BAROMETRIC VARIATIONS. 



At the April meeting of the Meteorological Society, Pro- 

 fessor J. K. Lausrhton oave some of his conclusions on the 

 nature and cause of the diurnal variation of the barometer; 

 and although these views seem to be identical with those 

 maintained by Lamont, of Munich, as long ago as 1832, yet 

 it is worth while to revive their consideration in these days 

 when so much attention is directed to meteorological phe- 

 nomena. Laughton believes that the cause of the diurnal 

 variation is to be found, not in the different temperature and 



