The Philosophical Instruments in the Paris Exhibition. 429 



Several excellent cathetometers were exhibited. The most 

 delicate were those made by Bauer, of St. Petersburg, under the 

 direction of Professor Jacobi, and by Perreaux and Guillemot of 

 Paris. These instruments show with great accuracy the dis- 

 tance between two points in a vertical line to the 0*0002 of an 

 inch. A pantograph contrived by M. Gavard of Paris, who has 

 long been engaged in perfecting this instrument, was highly 

 deserving of notice for the new application that it involves. 

 By its means duplicate figures can be engraved on several copper 

 cylinders, and impressions taken from them. The invention is 

 likely to be introduced in the calico printing trade. 



The great attention devoted during recent years to meteo- 

 rology has led to considerable improvements in instruments for 

 registering meteorological phenomena. The exhibition of 

 these in Paris was very complete, comprising a great variety 

 of barometers, thermometers, anemometers, rain-gauges, etc. 

 By far the most important exhibition in this department was 

 that by Padre Secchi, Director of the Observatory in the 

 Oollegio Romano, who showed his automatic meteorological 

 apparatus, invented, and almost entirely constructed, by 

 himself. This, which is by far the best apparatus of the kind 

 in existence, registers, by means of curves traced on paper, 

 the temperature, pressure of the atmosphere, direction and 

 force of the wind, amount of rain, and humidity. The appa- 

 ratus, which is acted on by clockwork and voltaic currents, 

 performs admirably, and its registrations are worthy of the 

 greatest confidence. The construction of this elaborate and 

 highly ingenious apparatus is most creditable to Padre Secchi ; 

 and the more so, as he derives very little assistance from 

 Government funds. A new barometer was exhibited by the 

 inventor, Mr. Clum, of the United States. He has called it 

 the Aelloscope Barometer, from aeXka, storm, and (ncoire, to 

 view ; its object being to indicate the powerful atmospheric 

 vibrations which precede storms. It is certainly extremely 

 sensitive, but so complicated and costly, that it is not at all 

 likely to come into general use. The lowest price of this 

 instrument is 1000 dollars. A new mercurial barometer, of a 

 very sensitive nature, and extremely portable, was exhibited 

 by Messrs. Beck. It has been tested to a height of 14,0u0 

 feet, and found to be extremely accurate. 



The Aneroid Barometer,* which has become a very trust- 



* This instrument was invented by Coiite (known for the drawing-chalks 

 which bear his name), when he was director of tiie Aerostatic Establishment at 

 Meudon, founded by the first Napoleon for- campaigning purposes. Conte was 

 desirous to make a barometer that should be smaller and less liable to injury, 

 than the usual mercurial instrument ; but though he constructed that now known 

 as the Aneroid, he was not able to make it sufficiently precise to be depended 

 upon, and thus left it for Vidi and others to perfect it. 



