Intelligence and Miscellaneous Articles, 141 



account for the complete cessation of polarization. As a proof of 

 this, 1 bored a hole of about 3 mm. diameter so that the current 

 could partially traverse this aperture. By introducing this also 

 there was a considerable decrease of the current strength, and at 

 the same time a powerful disengagement of gas on both sides. I 

 have had the observations repeated by a student, Mr. John Daniell, 

 in such a way that, after introducing various metal partitions, the 

 deflexion of the galvanometer, in case there was any alteration, 

 could be restored to its original amount by reducing the resist- 

 ance. In these circumstances, for the same current strength, the 

 polarization at the terminal electrodes is unchanged and the 

 resistance taken out is proportional to the total polarization at the 

 metal partition*. 



In the investigation, besides the plates mentioned above, one was 

 used in which the aperture was covered with four superimposed 

 gold-leaves ; these formed apparently one plate. It was necessary 

 to remove in using : — 



Perforated platinum plate 5 Siemens units. 



Platinum plate 15 „ „ 



Silver-leaf ,, „ 



Gold-leaf „ „ 



,, „ fourfold 0*25 „ „ 



It will be of interest to examine the dependence of the strength 

 of polarization on the thickness and nature of the metal partition. 

 This Mr. Daniell intends to do in lny laboratory. — Verhandlungen 

 der Phys. Gesell. zu Berlin, No. 3, 1892. 



NOTE ON THE ABSORPTION OF RADIANT HEAT BY ALUM. 

 BY 0. C. HUTCHINS, BOWDOIN COLLEGE. 



It seems to be the generally accepted opinion that a solution 

 of alum acts as a particularly efficient absorber of rays of great 

 wave-length. It is certain that the alum cell is universally used 

 and recommended wherever a transparent medium is desired for 

 cutting off the so-called " dark " heat-rays. 



In the April number of this Journal (Am. Journ. Sci.) Mr. 

 F. J. Eogers states that the results of Julius Thomsen are in error 

 because Thomsen used pure water instead of alum solution as an 

 absorber. 



Whence this idea in regard to the effect of alum solution arose 

 it is difficult to say : I have searched in vain for any authority 

 for it. Melloni's table, as far as it goes, shows that bodies in 

 solution raise slightly the percentage of transmitted rays above 

 that which passes through pure water. 



I prepared a saturated solution of potash alum in distilled water 

 and placed it in a cell 0*6 cm. thick. The sides of the cell were 



* Of course with the exception of the perforated platinum plate, in 

 using which there is a short circuit in the cell. 



