280 , Scientific Intelligence. 



5. The Hydrates of Sodium Carbonate. — Wegscheider has 

 recently discussed the compounds of sodium carbonate with water 

 of crystallization, aud has reached the conclusion that besides the 

 stable salts Na 2 C0 3 .H 2 (theruionatrite) and Na 2 CO 3 .10H 2 O, 

 only one unstable hydrate, Xa o C0 3 .7H 2 has been certainly 

 established. A considerable number of other hydrates have been 

 described, all of which appear to have been mixtures of two 

 hydrates or of a hydrate with mother-liquor. — Zeitschr. (morgan. 



Chem., lxxiii, 256. h. l. w. 



6. Canadium. — In connection with the announcement men- 

 tioned in this department last month, of the discovery of " cana- 

 dium," a supposed new element of the platinum group, attention 

 has been called to " amarillium," an alleged new element discov- 

 ered by Courtis in a copper carbonate ore from the Frazer Claims, 

 Similakameen, British Columbia, in 1903.* This was described as 

 having properties somewhat similar to those of " canadium," and 

 it was believed to form a link between the platinum-palladium 

 and the iron-nickel groups of metals. Nothing further has been 

 heard of " amarillium," so that it may be presumed that it did 

 not prove to be a new element. — Chem. News, cv, 36. h l. w. 



7. The Intrinsic Brightness of the Starlit Sky. — Important 

 researches have been made in recent years on the number and 

 distribution in the sky of stars of different magnitudes. The sta- 

 tistical data which serve as a basis for the calculations are so 

 difficult to obtain that it is a matter of importance to find a direct 

 verification of them. Such a verification may be sought by meas- 

 urement of the mean intrinsic brightness of the sky in different 

 regions of the celestial sphere. In 1903 Townley applied photo- 

 graphic processes to the solution of this problem, but, since his 

 exposures required one hour, the method recently devised and 

 tested by C. Fabry seems preferable and very promising. 



The apparatus used is extremely simple, and it may be briefly 

 described as follows : A lens or telescope objective of focal 

 length 48 cm , and aperture 5 cm , is mounted at one end of a tube 

 which projects at its other end into a suitable box. This box is 

 closed on the inside by a transverse diaphragm, which is pierced 

 by a circular aperture whose diameter can be varied at will and 

 whose center coincides with the principal focus of the telescope 

 objective. On the side of the diaphragm more remote from this 

 lens an optical system of short focus and large aperture is affixed. 

 Because of the role which this system plays, Fabry calls it the 

 "microscope objective" and says : " It is not necessary that this 

 objective should have good optical qualities ; it consists, in my 

 apparatus, of two simple lenses, each of 20 dioptrics, forming 

 a system of focal distance /=3'15 cm , and of 3*5 cm usable diam- 

 eter." This lens system projects on a photographic plate an 

 image of the telescope objective. The image is uniformly illumi- 

 nated and of 3 mm diameter, irrespective of the diameter of the 



* Trans. Amer. Inst. Min. Engrs. , xxxiii, 347. 



