NATURAL PHILOSOPHY. 131 



upon the advantages which would attend the use of very small bars 

 in most magnetical investigations, and had employed excessively 

 minute needles in his galvanometers with great success. Dr. Joule 

 stated his intention to lit up his needle so as to be observed by light 

 reflected from its polished surface, or otherwise, by viewing a glass 

 pointer, attached to the bottom of the steel, through a microscope. 

 II;' believed that by the latter plan he should be able to observe 

 deflections as small as one second of an arc. 



Great Electro-Magnet. Messrs. Chester, of New York City, have 

 recently constructed an electro-magnet of unusual size, for the New 

 York Free Academy. It is made of the purest iron. The core is 

 four inches in diameter; its total length is five feet. The wire 

 wound upon it is in eight separate strands, and the aggregate weight 

 of copper is 200 pounds. The entire weight of the magnet is 650 

 pounds. It is arranged either to be suspended with the faces down- 

 ward, or to be placed upright on a wheeled platform. Connected 

 with it is apparatus for diamagnetic experiments, consisting of rotat- 

 ing copper discs and tubes. When the magnetic force is in action 

 the rotating disc is instantly stopped, and motion is converted into 

 heat. The heat evolved is sufficient to cause water to boil in a cop- 

 per tube. 



THE TELEGRAPH AS A METEOROLOGICAL INDICATOR. 



" The electric telegraph is likely to render us henceforth a service 

 which it has not until now been known to be capable of. For some 

 time past it has been systematically employed, to transmit to one 

 center meteorological observations made at a great number of widely 

 scattered points, and to transmit from that center predictions founded 

 on these observations ; but Father Secchi, the Italian savant, now 

 informs us that a line of telegraph wires itself constitutes a better 

 indicator of certain kinds of meteorological changes than any other 

 we as yet know of. All persons at all familiar with electric telegraphy 

 are aware that currents other than those proceeding from the batteries 

 employed are constantly passing along all lines of telegraph wires. 

 They are derived from either the earth or the atmosphere, and are 

 called ' earth-currents.' They are subject to great variations, which 

 Father Secchi and some of his friends have for some time past been 

 carefully studying, with the result, among others, of finding that, 

 whenever the earth-currents are more irregular than ordinary, bad 

 weather invariably follows, the degree of their regularity of the 

 earth-currents bearing always an exact relation to that of the storai- 

 iness of the weather which they precede. We are certainly progress- 

 ing as regards our power of forecasting meteorological changes." 



ON PERIODIC CHANGES IN THE MAGNETIC CONDITION OF THE 

 EARTH, AND IN THE DISTRIBUTION OF TEMPERATURE 



UPON ITS SURFACE. 



The following is an abstract of a very curious and interesting 

 paper recently read before the Manchester (Eng.) Philosophical So- 

 ciety, by Mr. Baxendall, F. R. A. S. He says : 



Considerations arising out of an investigation of the irregularities 

 which take place hi the changes of some of the variable stars, led the 



