METEOROLOGY. 405 



time, the latter being nearer the center of the town. Thus the process 

 has done the duty it was intended for, although only once tried for this 

 special purpose. I am looking to it as an agent specially for the ex- 

 amination of climate, but of course it may have many uses. This proc- 

 ess does not aim at delicacy, but at accumulation of effect. I have 

 not spoken of a standard ; the results are only comparative, but the 

 process may be made to supply its own standard." 



Since writing the above it appears that by using sulphuric acid some 

 of the fears at first entertained may be avoided. 



The strength of solutions and the kind of acid to be used may vary. 

 Similar results may vary b}^ using bromide of potassium, but it is less 

 delicate. The surface exposed and other questions require attention. 

 {ISfatiire, xxii, p. 71.) 



Professor Fornioni has recently described to the Instituto Lombard© 

 a simple nefodoscope or instrument for measuring the direction of motion 

 of clouds (the instrument of the kind known as that of Braun being 

 thought expensive and inconvenient to use). It consists of a flat com- 

 pass case, with pivoted needle, above which is fixed horizontally a 

 plane mirror, occupying the whole of the case. On the surface of the 

 mirror are drawn diagonal lines corresponding to the rose of winds. 



The amalgam is removed in a narrow circular arc extending from north 

 to northwest, so that the end of the needle may be seen for the purpose 

 of orientation, and this arc is graduated. A rod with terminal eye freely 

 pivoted on the edge of the case completes the instrument. 



When the direction of a given cloud is to be determined the nefodo- 

 scope is placed in a horizontal plane and properly oriented. The rod 

 is then moved to such a position that the observer's eyes see three 

 points in a straight line, viz, the eye of the rod, the center of the mirror, 

 and the reflected image of a selected point of the cloud. The direction 

 of the displacement which the latter undergoes (after a time propor- 

 tional to the velocity of the cloud, and inversely as its distance) is the 

 required direction. {Nature, xxii, p. 132.) 



Mascart communicates to the Paris Academy of Sciences a method 

 of measuring variations of gravity by utilizing the pressure of a given 

 mass of gas at constant temperature, and finds the method capable of 

 great precision. He uses a kind of siphon-barometer, with the short 

 branch closed and holding CO2, introduced at a pressure sufiBcient to 

 balance a mercury column of 1™ when the tube is vertical. The in- 

 strument is placed in a metallic cylinder filled with water, which is 

 agitated by an air-current, and contains a thermometer measuring j^q 

 degree. The divided scale is fixed on the tube; one sees it by reflec- 

 tion on a gilt surface, which sends the virtual image into the axis of the 

 tube, and tbe mercury is seen through the gold layer. Thus one can 

 see, with a single microscope, the mercury-level and the corresponding 

 division of the scale. {Nature, xxvi, p. 312.) 



