NATURAL PHILOSOPHY. 165 



succeeded in dexterously joining on a piece of glass tube to the broken 

 end. The tube in question is about thirty-four feet long, and it was 

 filled with water from which every particle of air had been driven by 

 a jet of steam from a boiler. The steam was permitted to pass into 

 the tube, which had its lower part situated in a vessel filled with dis- 

 tilled water, and upon a vacuum being formed in the tube, and its 

 top hermetically sealed, the water ascended in it to a height of thirty- 

 two feet nine inches. This is equivalent to a column of 28.84 inches 

 of mercury. As a change in the atmospheric pressure which causes a 

 variation of an inch in a column of mercury will cause a variation of 

 more than a foot in a column of water, so the changes in the latter 

 will be more than twelve times as great as in the former ; and many 

 oscillations of the atmospheric pressure, which otherwise would escape 

 observation, will be noticeable. In gales of wind and heavy storms, 

 the water inside of the long tube of Darnell's barometer trembles, and 

 sometimes moves rapidly up and down as if animated by a spirit. 



NEW PLUVIOMETER (RAIN-GAUGE.) 



Common pluviometers consist of a square funnel fixed on the top 

 of a roof, its narrow end being provided with a stopcock, and commu- 

 nicating with the interior of an apartment. The mouth of the funnel 

 is generally a square foot, or some other square measure, in size ; once 

 a day the stopcock is opened, and the water in the pipe measured in 

 pints, quarts, etc. We thus learn how much rain has fallen on a 

 square foot, or other measure, within the lapse of twenty-four hours ; 

 but this is all we know nothing of the duration of each shower, the 

 size of the drops, their number, etc. To supply this deficiency, M. 

 Herne Mangon, of Paris, has invented a new pluviometer, which he 

 calls a, pluvioscope, 



Suppose a long strip of paper to be rolled on a cylinder, and then 

 gradually unrolled by means of clockwork, so that in the course of 

 twenty-four hours every part of it may have been exposed to the open 

 air. It is evident that the length of paper unrolled will be propor- 

 tional to the length of time elapsed ; so that every hour and minute 

 may be marked upon the paper. Now if the latter be so prepared as 

 to receive the impression of a drop of rain, it is clear that its size and 

 the precise moment of its falling may be ascertained. M. Herne 

 Mangon prepares his paper with a solution of sulphate of iron, and 

 then, after it has become dry, rubbing it with finely powdered galls. 

 A drop of rain falling on paper thus prepared leaves a well-defined 

 black spot, which will reveal all the circumstances of the shower. If, 

 for instance, the spots are small and few, the shower has been a mere 

 sprinkle; if small and numerous, a quiet but rather obstinate shower; 

 if large, and many of them run into one another, the shower has been 

 a violent one. By this contrivance, M. Herne Mangon has ascer- 

 tained the number of showers that fell within given dates, and even 

 the number of drops that fell, on a given spot, during some of these 

 showers. For instance, he ascertained that on the 2Gth of last June, 

 at half past eleven, A. M., the number of drops which fell, -per hectare 

 (a space of about two and a half English acres), in one minute, was 

 one thousand eight hundred and twenty-six millions, the drops being 



