Limit of Light in the Ultra-violet part of the Spectrum. 13o 



Journals {continued). 



Medico-Legal Journal. Vol. VI. No. 3. 8vo. New York 1888. 



The Editor. 



Naturalist (The). Nos. 165-166. 8vo. London 1889. 



The Editors. 



Revista do Observatorio. 1889. Num. 2-3. 8vo. Rio de Janeiro. 



Imperial Observatory, Rio de Janeiro. 

 Revue Medico-Pharmaceutique. 1889. No. 2. 4to. Constantinople. 



The Editor. 



Stazioni Sperimentali Agrarie Italiane (Le). Vol. XV. Fasc. 3. 



Vol. XVI. Fasc. 1-3. 8vo. Roma 1888-89. The Editor. 



Technology Quarterly. Vol. II. No. 3. 8vo. Boston 1889. 



The Editors. 



Zeitschrift fiir Naturwissenschaften. 1887. Hefte 3-6. 1888. 

 Hefte 1-4. 8vo. Halle. 



Naturwissenschaftlicher Verein, Halle. 



,il On the Limit of Solar and Stellar Light in the Ultra-violet 

 Part of the Spectrum." By William Huggins, D.C.L., 

 LL.D., F.R.S. Received March 28 —Read April 4, 1889. 



It has been long known that the solar spectrum stops abruptly, but 

 not quite suddenly, at the ultra-violet end, and much sooner than the 

 spectra of many terrestrial sources of light. The observations of Cornu, 

 of Hartley, and, quite recently, of Liveing and Dewar, appear to show 

 that the definite absorption to which the very rapid extinction of the 

 solar spectrum is due, has its seat in the earth's atmosphere, and not 

 in that of the sun ; and that, consequently, all ex-terrestrial light 

 should be cut off at the same place in the spectrum. 



During several years I have attempted to obtain the limit in the 

 ultra-violet for stellar light here, but as it was necessary to make use 

 of a bright star at a high altitude, and at a time when the atmosphere 

 was very clear, it was not until September 20th, 1888, that I was able 

 to obtain a result which seemed to me to be satisfactory. 



On that night three successive photographs of Vega, with increas- 

 ing exposures, were taken on the same plate. The first spectrum was 

 exposed for 10 minutes, the second for 20 minutes, and the third 

 spectrum nearly four times as long, namely, for 70 minutes. 



A comparison of the extent of the second spectrum due to an 

 exposure of 20 minutes with that of the third spectrum, to which an 

 ■exposure of 70 minutes was given, leaves no doubt that the latter 

 spectrum has reached the limit imposed by atmospheric absorption, 

 and has not stopped in consequence of an insufficient exposure of the 

 plate. 



