76 Intelligence and Miscellaneous Articles, 



to detect tears in glass in the proper sense of the word ; and the 

 result was, that in thick plates of glass, such as are used for making 

 ordinary spectacle-glasses, a square inch of perfectly homogeneous 

 glass was sought in vain. Those tears were found most injurious 

 which in the apparatus presented the appearance of a surface covered 

 with fine pencil- marks. 



Irregularities in density in the air which were produced by ascend- 

 ing warm air could be recognized even if the difference in tempera- 

 ture of the warm body and of the surrounding air only amounted to 

 0°*6. Unequally warmed or pressed glass also exhibited distinct 

 tears. For a study of the issue of different gases into the air the 

 apparatus was also used ; and it was observed that a jet of coal-gas 

 ascending vertically preserved a coherent cylinder for a longer time 

 than carbonic acid which descended vertically. The evaporation of 

 alcohol, even at the temperature of 0° C, could be detected by means 

 of the apparatus. The investigation of flame showed that, besides 

 the different envelopes which are visible to the naked eye, there is 

 an external one which surrounds the entire flame and obviously arises 

 from the heated air. 



To the observation of the electric spark the author devoted espe- 

 cial attention, and the view was confirmed that the spark in jumping 

 across rarefies the air. It is of especial interest to observe how the 

 sound-waves become visible in the apparatus when the sound is 

 produced by the jumping spark ; the author by the naked eye could 

 even observe the diffraction, refraction, and reflection of sound. Un- 

 fortunately he did not succeed in contriving an objective representa- 

 tion of these phenomena. — From a Review in the Fortschritte der 

 Phi/siJc,xol. xx. of a pamphlet published by the author at Bonn in 1864. 



OBSERVATIONS ON CERTAIN LINES OF THE SOLAR SPECTRUM. 

 BY M. ANGSTROM. 



I have read with great interest a note by M. Janssen on the 

 telluric rays of the solar spectrum, in which the author points out a 

 mode of experimentally obtaining these. Having been occupied for 

 more than three years with the determination of the wave-lengths 

 of a great number of Fraunhofer's lines, I have frequently had occa- 

 sion to observe the telluric rays, and that under circumstances 

 rarely offered to observers who are placed in a lower latitude than 

 that of Upsala. 



M. Janssen says, in his note, that aqueous vapour produces in the 

 solar spectrum five groups of obscure lines, extending from D to A, 

 and among which would be found the group A and a great part of 

 B. I also think that A and B are telluric lines; but they are not 

 due to aqueous vapour. The following are the facts on which I 

 rely. During the great colds of January 1864, I several times ob- 

 served the solar spectrum at Upsala, and once at a temperature of 

 — 27° C. The telluric lines near D, C, and a, as well as those from a 

 to B, had almost entirely disappeared ; while the groups A and B, 

 and a third, situated near the middle between B and C, and which 

 Sir D. Brewster designates by the letter C, were very intense, more 

 so even than they were in summer for the same height of the sun. 



