V. DLSCHAUGK. 277 



1375a. Air Thermometer after Riest. 



Ifarmbrunn, Quilitz, > Co., Berlin. 



1375b. Spark Micrometer after Riest. 



Warmbrunn, Quilitz, $ Co., Berlin. 



1376. Apparatus used by M. Rijke to measure the distances 

 at which the Ley den jar explodes. 



Professor Dr. P. L. Rijkc, Ley den. 



1377. Vacuum Tube for electric discharge. 1856. 



Teyler Foundation, Haarlem. 



Masson in Paris used a Torricellian vacuum sealed by the lamp, in his 

 extensive researches on the electric spectrum. Some time afterward, Mr. 

 Geissler, in Amsterdam, made this Torricellian vacuum at the instigation of 

 Prof. Van der Willigen, now director of the Teyler Museum, whose property 

 it is at present. The experiments with this tube are described in Poggen- 

 dorffs Annalen, vol. xcviii. p. 487, 1856. Subsequently Mr. Geissler in Bonn 

 constructed his various well-known and beautiful tubes. This tube contains 

 a little mercury and carbonic oxide gas. 



1377a. Four Geissler's Vacuum Tubes. E. Cetti and Co. 



137 7b. Collection of Geissler 3 s Tubes. 



Dr. H. Geissler, ttonn. 



1377c. 1. Apparatus for the Production of Hydrogen 

 Gas. 



2. Tube, by Geissler, for two gases. 



o. Tube, by Geissler, forming a diadem. 



4. Tube, by Geissler, forming a diadem. 



5. Tube, by Geissler, with inner spiral. 



6. Tube, for liquids, with six spirals. 



7. Phosphorescent tubes, set in the form of writing. These 

 tubes preserve their brilliancy in the darkness long after being- 

 exposed to solar light. 



Alvergniat Freres, Paris. 



1377d. Three Vacuum Tubes, to show the connexion 

 between the resistance of rarefied air and the phenomenon at the 

 cathode, the so-called negative glow. Prof. Ilittorf, Munster. 



Apparatus (A) made by Dr. Geissler, of Bonn, consists of two balls which 

 communicate together by two tubes of equal width, one short and one of 

 spiral form 3^ metres long. The electrodes of aluminium wire pass through 

 the balls and end in the short tube so that there is a free interval of only 

 2 mm. between them. The opening current of the Rhumkorff coil passes, in 

 consequence of the great rarefaction of the air in the tube, not by this short 

 path, buj; prefers the longer one. If the latter, by closure of the glass cock, 

 be stopped, the passage is effected, but only with much greater tension, by 

 the short interval. The tube (B) has the same arrangement, but without the 

 glass cock. It is used in place of (A) where the air is able to penetrate and 

 the required vacuum ceases. The glass vessel (C) consists of a wide reservoir 



