ASTRONOMY. 131 



Langley^s observations of hitherto iinreeognized umve-lengths. — Profes- 

 sor Langlej^ having traced the solar spectrum iu the infra-red as far as 

 wave-length =0.0027 of a millimeter, where it suddenly ceased, has 

 since, with more delicate instruments, examined the emission spectra 

 of various terrestrial substances at temperatures from that of fusing 

 platinum to that of melting ice, and more particularly of temperatures 

 corresponding to the ordinary conditions of the soil. The result has 

 been to show that the maximum of heat from cold and black bodies has 

 in every case a wave-length greater than 0.0027 — greater, that is to say, 

 than that of the lowest solar heat which reaches us. Professor Lang- 

 ley thus sums up (Am. J. Sc, 132 : 84-106) his investigation : " Broadly 

 speaking, we have learned through the present measures with certainty 

 of wave-lengths greater than 0.005 millimeter, and have grounds for es- 

 timating that we have recognized radiations whose wave-length ex- 

 ceeds 0.03 millimeter, so that while we have directly measured to nearly 

 eight times the wave-length known to Newton, we have probable indica- 

 tion of wavelengths far greater, and the gulf between the shortest vi- 

 bration of sound and the longest known vibration of the aether is now 

 in some measure bridged over." 



The visual solar spectrum in 1884. — Professor Piazzi Smyth made a 

 careful map of the solar spectrum in 1884 in order to determine whether 

 any perceptible effect had been produced by the " white skies" so prev- 

 alent in that year. His observations have lately been published in a 

 series of sixty plates, in the Transactions of the Eoyal Society of Edin- 

 burgh, vol. 32. He finds that the red and violet ends of the spectrum 

 show a marked general dulling, such as should arise from the upper 

 air being laden with minute opaque particle^} — whether from the Kra- 

 katoa explosion or any other source. 



Thollonh map of the solar spectrtim. — M. Thollon, in the Bulletin as- 

 tronomique for July, gives some interesting details in regard to the 

 great map of the spectrum for which the Lalande prize of the Paris 

 Academy was awarded him about a year ago. An earlier map from A 

 to H was finished by Thollon in 1879, but he determined to go over 

 the work again with improved instruments, and to make a chart 

 representing, with all the accuracy attainable, the positions, breadths, 

 and relative intensities of the lines, a chart which will enable us to 

 determine in the future whether any changes have taken place. For 

 even now, from the comparison of M. Thollon's chart with that of Angs- 

 trom, there is a strong suspicion that some change has occurred in the 

 intensity of several lines between B and C. 



M. Thollon has carried the map from A to b, and it is to be continued 

 to the violet by M. Trepied. It is now more than 33 feet long (though 

 it covers little more than one-third of the spectrum), and contains 

 about 3,200 lines, nearly 900 of which are distinguished as of telluric 

 origin. The instrument employed was a large spectroscope with bi- 



