NATURAL PHILOSOPHY. 173 



exhibited several specimens. The first of these consisted in the employment 

 of platina instead of copper, and of making a skeleton figure roughly re- 

 sembling the outline of the cast sought to be attained, by means of which, 

 according to the lecturer's process, can be produced busts, statues, and 

 groups in full relief by a single operation. The second process was for gal- 

 vanizing or coppering iron and cast iron to any thickness required without 

 the cyanide bath, and its employment in commerce and in the navy. The 

 process was not fully communicated, as it is commercially desirous to keep 

 it a secret, but sufficient was communicated to show that the cvanide bath. 



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which is not only expensive but dangerous, can be dispensed with. The 

 last branch of the paper treated of Messrs. Christofi and Bouillet's proce.-.> 

 for strengthening electrotypes, the principle of which was to leave an open- 

 ing in the back of the thin electrotype, obtained by precipitating it, and by 

 putting it into a number of small pieces of brass, which, on being melted 

 with an oxhydrogen blast, become diffused all over the interior of the cop- 

 per without injuring it in any way, and thereby imparting to it' the strength 

 of cast iron. 



RECENT PROGRESS OF TERRESTRIAL MAGNETISM. 



It has been long known that the elements of the earth's magnetic force 

 were subject to certain regular and recurring- changes, whose periods were, 

 respectively, a day and a year, and which, therefore, were referred to the sun 

 as their source. To these periodical changes Dr. Lament, of Munich, 

 added another of ten years, the diurnal range of the magnetic declination 

 having been found to pass from a maximum to a minimum, and back again, 

 in about that time. But besides these slow and regular changes, there are 

 others of a different class, which recur at irregular intervals, and which are 

 characterized by a large deviation of the magnetic elements from their nor- 

 mal state, and generally also by rapid fluctuation and change. These phe- 

 nomena, called by Humboldt " magnetic storms " have been observed to 

 occur simultaneously in the most distant parts of the earth, and therefore indi- 

 cate the operation of causes affecting the entire globe. But, casual as they, 

 seem, they are found to be subject to laws of their own. Professor Kreil 

 was the first to discover that, at a given place, they recurred more frequently 

 at certain hours of the day than at others ; and that, consequently, in their 

 mean effects, they were subject to periodical laws, depending upon the hour at 

 each station. The laws of this periodicity have been ably worked out by 

 General Sabine in lib discussion of the results of the British Colonial Ob- 

 servatories ; and he has added the important facts, that the same phenomena 

 observe also the two other periods already noticed, namely, the annual and 

 the decennial periods. He has further arrived at the very remarkable result, 

 that the decennial magnetic period coincides, both in its duration and in its 

 epochs of maxima and minima, with the decennial period observed by 

 ' Schwabe in the solar spots ; from which it is to be inferred that the sun ex- 

 ercises a magnetic influence upon the earth dependent on the condition of its 

 luminous envelop. We are thus in the presence of two facts, which appear 



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