434 Chronicles of Science. [July? 



The following results have been obtained by M. Becquerel in 

 some researches on the variations of temperature of the ground at 

 different depths, made by the aid of the electric thermometer. At 

 1 metre beneath the surface of the ground the mean temperature 

 varies between winter and summer as in the air. The difference 

 between the maximum and the minimum is 6° C. in the ground, and 

 18" 17° in the air. At 6 metres deep the variations occur in the 

 inverse order, the maximum taking place in winter, and the difference 

 between the maximum and the minimum being 1°. At 11 metres 

 deep the variation is not more than 0*3° ; the maximum takes place 

 in winter, the minimum between the spring and summer. From 

 16 to 26 metres the variations follow the same law as in the air, 

 with this difference, that the difference between the maximum and 

 the minimum is only 027° C. This anomaly or inversion of the 

 law is due to the infiltration of water through permeable strata. 

 Between 26 and 31 metres the variations follow the laws the op- 

 posite to those of the air. Below 31 metres the variations of 

 temperature attain scarcely 0-12°, the temperature being sensibly 

 constant. 



General Morin has described an electro-thermometric register 

 for marking automatically, every quarter of an hour, the variations 

 of temperature in an enclosed spot or in the open air. Some ex- 

 cellent forms of apparatus have already been invented and put to 

 use for registering the variations of temperature, not only inter- 

 mittently, but continuously. 



A very ingenious as well as commercially valuable form of 

 caloric engine has been lately exhibited in London. In principle it 

 is based upon the fact, long known to scientific engineers, that the 

 most economical mode of obtaining power from heat is by its direct 

 application to the expansion of air, or other permament gases, rather 

 than by that of steam or any other vapour. The hot-air engine 

 now described differs, however, from the usual form of caloric 

 engine in several essential particulars as to its construction, so that 

 it is free from those defects which have hitherto prevented the 

 practical carrying out of the caloric theory. In this engine the 

 motive power, instead of being derived from the expansion of air 

 heated in a separate generator as in former engines, is produced by 

 the expansion of air heated by contact with the fuel itself; and in 

 addition to this source of the power, by the action of the expansive 

 force of the gaseous products of the combustion of the fuel, which 

 heretofore have been permitted to escape into the chimney without 

 being in any way utilized in the production of power. This result 

 is accomplished by placing the fuel in a grate which can be her- 

 metically closed, and forcing into it the air required for combustion 

 by means of an air-pump worked by the engine itself, so that no 



