400 Intelligence and Miscellaneous Articles, 



first very rapidly ; then for a certain time it goes on slowly ; and 

 then again follows a period of rapid augmentation. 



With the cast-iron bars, the second period of rapid increase is also 

 observed, but in a less marked degree, but with the wrought iron it 

 does not exist. 



The author believes he may conclude from his experiments, that 

 the magnetic properties of iron are developed suddenly at a determi- 

 nate temperature. This might be caused, according to M. Mauritius, 

 by a sudden change in its chemical constitution ; that is to say, 

 at a certain temperature iron may pass from the biatomic to the 

 monatomic condition, and the biatomic condition is that in which 

 magnetism can alone exist. Further, the second period of rapid 

 increase of magnetism may be due to a similar change of chemical 

 constitution, in which the carbon would take part. — Bibliotkeque 

 Universelle de Geneve, March 1864 ; Poggendorff s Annalen, Novem- 

 ber 1863. 



ON THE ARTIFICIAL PRODUCTION OF ASTERISM. 

 BY C. A. GRUEL, OF BERLIN. 



The simple method by which the above phenomenon may be pro- 

 duced, in a manner as clear and perfect as is met with in some of the 

 naturally occurring minerals, is as follows. 



A clear piece of plate glass is cut in the form of an equilateral tri- 

 angle, with sides measuring l^to 2 inches, by means of a paper pattern 

 of these dimensions placed underneath. The surface of this triangle is 

 then rubbed backwards and forwards a few times on a sheet of fine emery 

 paper ; each of the three sides being successively guided against a 

 metal rule, which at the same time, being pressed on the emery paper, 

 keeps it in position. The feeble striping of the glass surface thus 

 obtained produces accurately the condition of a series of lines cross- 

 ing at an angle of 60°, which is fulfilled by the similarly directed 

 edges of the groups of microscopic crystals observed in some kinds 

 of mica, &c. 



As the diffraction experiments are among the most splendid of 

 optical phenomena, it is conceivable that a similar regular striping, 

 but effected with accurate machines, will produce a six-, eight-, or 

 multifold star according to the angle under which the gratings cross ; 

 and the glass piece thus prepared must infinitely excel both in beauty 

 of action and in the production of actual coloured spectres ; whereas 

 here, from irregular striping, the spectra are superposed, and only 

 represent the well-known star formed of bright radial lines like the 

 star of mica, &c* — Poggendorff's Annalen, November 1863. 



* I may mention that G. Rose (Poggendorff's Annalen, vol. cxvii. p. 635) 

 has also produced asterism by isinglass impressions of mica.— Poggen- 

 D jrff. 





