220 Prof. Drapers Description of the Tithonometer. 



tains them, at a distance of several inches, there is no difficulty 

 in understanding why a similar effect should take place with a 

 violent explosion when the discharge is made through their midst; 

 nor how a great many mixtures may be made to unite under the 

 same treatment. A flash of lightning cannot take place, nor an 

 electric spark be discharged, without chemical charges being 

 brought about by the radiant matter emitted.* 



Proofs of the exactness of the indications of the Tithonome- 

 ter. — The foregoing examples may serve to illustrate the extreme 

 sensitiveness of the tithonometer ; I shall next furnish proofs that 

 its indications are exactly proportional to the quantities of light 

 incident on it. 



As it is necessary, owing to the variable force of daylight, to 

 resort to artificial means of illumination, it will be found advan- 

 tageous to employ the following method of obtaining a flame of 

 suitable intensity. 



Let A B, fig. 4, be an Argand oil-lamp, of which the wick is C. 

 Over the wick, at a distance of half an inch or thereabouts, place 

 a plate of thin sheet copper, three inches in diameter, perforated 

 in its centre with a circular hole of the same diameter as the wick, 

 and concentric therewith. This piece of copper is represented at 

 d d ; it should have some contrivance for raising or depressing it 

 through a small space, the proper height being determined by 

 trial. On this plate, the glass cylinder e, an inch and three quar- 

 ters in diameter and eight or ten inches long, rests. 



When the lamp is lighted, provided the distance between the 

 plate dd and the top of the wick is properly adjusted, on putting 

 on the glass cylinder the flame instantly assumes an intense 

 whiteness ; by raising the wick it may be elongated to six inches 

 or more, and becomes exceedingly brilliant. Lamps constructed 

 on these principles may be purchased in the shops. I have, how- 

 ever, contented myself with using a common Argand study-lamp, 

 supporting the perforated plate d d at a proper altitude by a retort 



* Since the above was printed in London, I have found that there is no difficulty 

 in making chlorine and hydrogen explode, by passing the spark from a Leyden jar 

 of the capacity of a quart, outside the sentient tube of the instrument. This result 

 therefore confirms the views here expressed, that combinations ensuing on the pas- 

 sage of an electric spark are not entirely due to any such mechanical agency as 

 condensation or percussion, but to the action of the radiant matter emitted. I be- 

 lieve it will be found, that the explosive union of oxygen and hydrogen by an elec- 

 tric discharge is a phenomenon of the same kind. 



