252 METEOROLOGY AND ALLIED SUBJECTS. 



Eiegler,in «a discourse before the Austrian Meteorological Association, 

 lias urged the wider introduction of Piche's evaporimeter. The neces- 

 sity of some form of this instrument has been widely felt, but none of 

 the many devices have given satisfaction, or have been considered as 

 much better than local experiments. The comparison and study of these 

 instruments (especially that of Piche) have been especially undertaken 

 by Dr. Loreuz. The apparatus is made by Baudin and Tonnelot, in 

 Paris, and its prominent feature is a long glass tube, about one cen- 

 timeter in diameter, which is closed above, and hangs from a hook, 

 while the lower end is oi)en and ground off to a plane surface. On this 

 glass tube a scale is etcaed. The tube being filled with water, and the 

 lower end closed by a thin piece of filter paper, in which, if necessary, 

 fine needle holes have been pricked, the instrument is hung up in an 

 exposed place, and the amount of the continual evaporation of water 

 from the paper surface is easily determined by reading from the scale 

 etched on the tube. 



The inventor originally assumed that the evaporation from the wet- 

 paper surface is the same as from the free surface of water. But this 

 is not strictly true; and the relation between the indications of any 

 Piche instrument and a normal evaporimeter must bi^ determiued by 

 comparative readings; especially does the small size of the tube allow 

 the water therein to become easily heated, so that these instruments in 

 general have a much larger evaporation than the normal or standard, 

 which consists of a large cylinder of water established in a shady spot, 

 and so sunk within a still larger mass of water that the inner vessel 

 retains a uniform temi^erature. 



Eiegler states that his experiments have shown the necessity, on the 

 one hand, of accurate observation of the temi^erature of the surface of 

 large areas of water ; and further, that we must relinquish our attempt to 

 keep the water in our evaporimeter exposed under so-called natural 

 conditions, for we cannot possibly define what those conditions are. 



Not only is the Piche evaporator affected too easily by an excess of 

 temperature, but it is also liable to be troubled by atmospheric electric- 

 ity, and is, of course, utterly useless when the temperature falls below 

 freezing. These disadvantages partially counteract the great advantage 

 of simplicity of construction, and accuracy of its readings; and it is to 

 be hoped that, at least during the warmer portion of the year, this cheap 

 and simple instrument may be widely introduced. — {Z. 0. G. M., XIY, 

 p. 370.) 



The brief description given in 1878 of Nipher's modification of the 

 rain gauge has been supplemented hy the publication in full of his orig- 

 inal paper read before the American Association for the Advancement 

 of Science. Already in 1861 Jevons had clearly explained that any re- 

 sistance experienced by a current of air forces the latter to flow over the 

 sides and surface of the obstacle with increased velocity; consequently 

 the drops of rain that in the absence of this disturbance would have 



