150 ANNUAL OF SCIENTIFIC DISCOVERY. 



Having at hand everything necessary for a prompt verification, I proceeded 

 as follows : 



Between the poles of a powerful electro-magnet I partially engaged the 

 solid of revolution belonging to the rotatory apparatus which I have called a 

 gyroscope, and which I had previously used in experiments of quite another 

 nature. This solid was a torse of bronze, connected by means of a toothed 

 pinion to a moving wheelwork, and which, turned by means of a handle, 

 may attain the speed of 150 to 200 turns per second. To render the action 

 of the magnet more efficacious, two pieces of soft iron superadded to the 

 bobbins prolong the metallic poles and concentrate them in the vicinity of the 

 turning body. 



When the apparatus is at full speed the current of six Bunsen elements 

 directed into the electro-magnet, arrests the motion in a few seconds, as if an 

 invisible bridle had been applied to the motive power ; this is Arago's expe- 

 riment developed by Faraday. But if we then strain at the handle, in order 

 to restore to the apparatus the motion which it had lost, the resistance expe- 

 rienced, compels us to exert a certain degree of force, the equivalent of which 

 reappears arfd is effectively accumulated in heat in the interior of the turning 

 body. 



By means of a thermometer buried in the mass we follow, step by step, the 

 progress in elevation of temperature. 



Having taken, for example, the apparatus at the surrounding temperature 

 of 16 C. (60 8' R), I saw the thermometer rise gradually to 20 C. (68 P.), 

 25 C. (77 R), 30 C. (86 R), and 34 C. (93 2' R) ; but the phenomenon 

 was so much developed as not to require the employment of thermometrical 

 instruments ; the heat produced had become sensible to the hand. 



A few days afterwards the battery being reduced to two elements, a flat 

 disc formed of red copper was raised in two minutes' action to the temperature 

 of 60 C. (140 R). 



If this experiment appears interesting it will be easy to arrange an 

 apparatus for fully developing the phenomenon which I have noticed. Un- 

 doubtedly, by a suitably constructed machine composed only of permanent 

 magnets, we may produce elevated temperatures and exhibit to the public 

 assembled in lecture theatres a curious example of the conversion of labor 

 into heat. 



TERBESTRIAL MAGNETISM. 



As early as 1825, Col. Sabine had inferred, that an influence was exerted 

 by the sun and moon on terrestrial magnetism. In a set of observations 

 taken at the whiter station of one of the polar expeditions, where the declina- 

 tion was about 90, and discussed by him, it was remarked that when the 

 sun and moon were on the meridian at the same time, the diurnal variation 

 reached 5, but when they were at right angles to each other, this quantity fell 

 as low as 20. The sagacity Col. Sabine exhibited in his inference from this 

 isolated set of observations has been sustained by the laborious and patient 

 observations and investigations of fifteen years. Some quantities so minute are 

 developed in the researches, that a less time would hardly have served to 



