Intelligence and Miscellaneous Articles. 523 



dividual elements may be calculated from the present observations. 

 The values I found are : — 



H. 



9-0 



0'. 

 129-0 



0". 



17-0 



0'. 

 145-2 



C". 01,. Cl„. 

 98 282 249 



ci,„. 



218 



O'liy. 



194 



Br,. 

 413 



Br„. 



374 



Br,,,. 

 334 



I,. I„. 



642 577 



s,. 

 284 



7. The atomic magnetisms of the halogens decrease as the number 

 of atoms increases. — Wiedemann's Annalen, No 5, 1888. 



ON THE INSULATING ACTION OF VAEIOUS SUBSTANCES IN 

 RESPECT OP RADIANT HEAT. BY H. C. VOGEL. 



The heat from a Locatelli's lamp fell upon a sensitive thermo- 

 pile, which was within a metal box with double sides filled with 

 water, and only opened towards the lamp. In front of this the 

 materials to be investigated were placed in the form of plates. 

 The trans missibilifcy of the various substances was measured by 

 the increase of temperature which the front solderings experienced 

 when a stationary condition had been established. 



The screening action of the polished metals was greatest ; the 

 thickness of the metal layer was almost entirely without in- 

 fluence. Grlass and ebonite kept heat off the least. The most 

 perfect protection was afforded by several polished plates separated 

 from each other by layers of air. The following table gives the 

 increase of temperature over that of the surrounding air which 

 was attained with the various materials : — 



Glass C3-3 mm. thick) 10°9 



Ebonite (5-0 „ „ ) 8*7 



Pine wood (5-9 „ „ ) 6-6 



Pelt (7-5 „ „ ) 4-9 



Brass (0-2 to 0'4 mm. thick) 1-0 



Tin foil (0-02 mm. thick) 0-7 



Lead foil (0-08 „ „ ) 0-7 



Double screen of tin-plate with an air-space . 0-2 



Direct radiation gave in the galvanometer 30°. Hence, if on a 

 system (for instance pillars which support instruments) slow 

 changes of temperature are to be transmitted as uniformly as 

 possible, they must be protected by bad conductors ; rapid local 

 changes of temperature, for instance, such as are caused by the 

 bodily heat of the observer or by the lamps) are best kept off by 

 polished metal screens, behind which the air can circulate freely. 



As regards protection against changes in the external tempera- 

 ture, similar rules hold generally, except that in this case the 

 thickness of the protecting layer comes into play. — Astron. Naeh- 

 richt. vol. cxviii. p. 97. — Beiblatter cler Physilc, No. 4, 1888. 



