194 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



independent of such momentary changes in the strength of 

 the current as affect the readings of a magnetic needle. It 

 is also portable and inexpensive. Jour. Soc. Teleg. Engineers, 

 1875,296. 



THE ACTION OF AN ELECTRO-MAGNET UPON THE SPECTRA OF 

 RAREFIED GASES TRAVERSED BY ELECTRIC DISCHARGES. 



M. Cheautard states that he has examined the spectra of 

 rarefied gases illuminated by an electric spark, and subjected 

 to the influence of powerful magnets, and finds that these 

 spectra are characterized as to the position, the number, 

 the separation, and the fineness of their lines by very curious 

 traits peculiar to each gas. As regards the metalloids with 

 which only his experiments have thus far been conducted, 

 he states that the light given out by sulphur and by seleni- 

 um experienced a notable diminution under the influence of 

 the magnet, so that sometimes the spectrum, which was very 

 apparent at first, disappeared for some moments. On the con- 

 trary, chlorine and bromine are characterized by an increase 

 in brilliancy, and by the development of fine brilliant rays 

 especially numerous in the green, whose appearance or dis- 

 appearance at the moment when we turn on or interrupt 

 the current has a truly magical effect. This phenomenon 

 seems to have some importance in consideration of the ob- 

 scurity which at present characterizes our knowledge of the 

 relation of magnetism and light. 1 j5, 1875, 283. 



THE FREEZING OF SALT WATER. 



Professor Guthrie, in continuation of former researches on 

 the solutions of salt, has endeavored to ascertain the manner 

 in which mixtures of salt act as cryogens, and to study their 

 combination with water at various temperatures and in va- 

 rious proportions. He finds that when two salts, composed 

 of different acids or bases, are mixed, and no precipitation 

 occurs, it is generally considered that partial decomposition 

 takes place, two new salts being formed ; but he finds that 

 if the salts a x and b y be mixed in atomic proportion, 

 and dissolved in the smallest possible amount of water, a 

 mixture is obtained identical with that produced on mixing 

 a y with b x; and the temperature and composition of the 

 resulting cryohydratc are the same in both cases. Tims, a 



