Intelligence and Miscellaneous Articles. 22? 



With a little practice this measurement is susceptible of great 

 precision if a good spectrophotometer is employed. The new in- 

 strument which I use, constructed by M. Duboscq according to 

 the directions of M. Crova, leaves nothing to be desired in this 

 respect. 



The lamp employed is the Carcel standard, placed on the auto- 

 matic balance of M. Deleuil, the course and regulation of which 

 have been previously investigated*. The intensities obtained are 

 reduced to a normal consumptiou of 42 grammes of oil per hour. 



My researches have been directed to the spectrum of hydrogen, 

 which has the advantage of giving very pure lines situated in dif- 

 ferent regions of the spectrum. The spectrum-tube, with alumi- 

 nium electrodes, was illuminated at the commencement of the 

 researches by the spark of an ordinary Euhmkorff coil actuated by 

 three Bunsen elements, and later by a Holtz machine. To effect 

 the variation of the calorific energy of the spark, I confined myself 

 at first to interposing in the inducing circuit variable lengths 

 (B=14, 10, 6, 2 centim.) of fine German-silver wire. This first 

 disposition permits the direction of the phenomenon to be distinctly 

 seen ; it has been replaced (for some definitive measurements in 

 course of execution) by another, more precise. 



The gas-tube can be put into communication, by a three-way 

 cock, either with a system of tubes containing phosphoric anhydride 

 communicating with a pure-hydrogen generator or with the appa- 

 ratus for producing the vacuum. The initial step is the production 

 of the vacuum by means of Alvergniat's mercury pump ; it is com- 

 pleted by means of a mercury trompe with six falls, constructed by 

 MM. Aivergniat freres. "With the aid of this fine apparatus all the 

 pressures comprised between 7 millim. (at which the spark begins 

 to pass) and 0-000001 of an atmosphere are obtained. MacLeod's 

 gauge, attached to the instrument, accurately measures those 

 pressures. 



Here are some of the series obtained for the lines Ha, H/3, Hy, 

 on varying the pressure and the energy of the discharge (the inten- 

 sity of the corresponding regions of the lamp-spectrum, with the 

 nicols parallel, being arbitrarily put = 1000) : — 



Lines. 



Pressure , A ^ 



6-5 millim. Red. Blue. Violet. 



E 14 3-6 5-5 17-2 



B 10 6-2 7-5 18-1 



E 6 7-5 12-4 19-6 



B 2 9-5 22-6 36-7 



Lines. 



Pressure , A > 



0-542 millim. Bed. Blue. Violet. 



B 14 8-8 25-8 65-8 



B 10 12-9 34-2 868 



B 6 28-3 72-5 140-2 



B 2 49-4 1521 240-9 



* "Determination du pouvoir 6clairant des radiations simples," par 

 MM. Crova et Lagarde, Journal de Physique, [2] i. 1882. 



