134 ANNUAL OF SCIENTIFIC DISCOVERY. 



Were subject to the passage of currents of electricity, and therefore 

 granting the assumption that the passage of the electric current 

 changed the character of the iron there was a link wanting in the 

 chain of reasoning, inasmuch as it was not proved that axles were 

 subject to this electrical influence. Moreover, he was inclined to 

 doubt whether, if a piece of iron was at first perfectly fibrous, vibra- 

 tion would ever change the structure of the metal. The beams of 

 Cornish engines, for example, were subject to vast pressure ; they 

 never become crystallized: the connecting-rod of a locomotive was 

 subject to great vibration, strain, and pressure, vibrating eight times 

 a second when the velocity is forty miles an hour ; he had watched the 

 wear of a rod for three years, and no change was perceptible in the 

 structure of the iron. 



SELF-REGISTERING MAGNETIC NEEDLE. 



ONE source of error has constantly attended magnetic observations 

 in the most perfectly constructed observatories. The approach even 

 of the observer has been sufficient to produce a disturbance in the 

 magnetic needles or bars. This error, however, no longer exists. 

 Each magnetic bar is made to carry a little mirror, which reflects the 

 light of a lamp upon a piece of photographic paper kept constantly 

 moving behind an opaque plate having but one small vertical opening. 

 On this, for every minute of the twenty-four hours, each vibration of 

 the needle is faithfully recorded. The chemical radiations of an 

 Argand lamp supply the observer's place ; and at the same time, as 

 it records every change in the phenomenon of terrestrial magnetism, 

 it is made to mark the most delicate alternations in atmospheric 

 pressure, and to note every increase or diminution of temperature. 

 At Greenwich, the magnets, the barometers, and the thermometers 

 are all registered by the chemical power of light ; and M. Faye and 

 Gonjon, at Paris, knowing the error of the human eye in observations 

 on a bright object, have substituted the Daguerreotype plate for the 

 purpose of ascertaining the actual diameter of the sun, and they pro- 

 pose to the principal observatories of Europe to determine by a similar 

 method the absolute time. Electricity now determines the longitude, 

 and marks the transit of a star, and the sun's, rays perform equally im- 

 portant offices to aid the natural philosopher in his delicate research 

 for the truths which are as yet obscure. London Aihen&um, March. 



MAGNETIZED BRASS. 



REV. MR. RANKIN stated at the last meeting of the British Asso- 

 ciation, that he had found the northern half of a brazen meridian of a 

 celestial globe to be so strongly magnetic as to deflect a small needle 

 placed near it so much as eight points from its true direction, while 

 the southern part of it seemed to be wholly free from magnetism. 

 London Athen&um. 



