Professor Draper's Description of the Tiihonometer. 403 



The experimenter may further assure himself of the ex- 

 treme sensitiveness of this mixture by placing the instrument 

 before a window, and endeavouring to remove and replace 

 its screen so quickly that it shall fail to give any indication ; 

 he will find that it cannot be done. 



Charge a Leyden phial, and place the tithonometer at a 

 little distance from it, keeping the eye steadily fixed on the 

 scale ; discharge the jar, and the rays from the spark will be 

 seen to exert a very powerful effect, the movement taking 

 place and ceasing in an instant. 



This remarkable experiment not only serves to prove the 

 sensitiveness of the tithonometer, but also brings before us 

 new views of the powers of that extraordinary agent electri- 

 city. That energetic chemical effects can thus be produced 

 at a distance by an electric spark in its momentary passage, 

 effects which are of a totally different kind from the common 

 manifestations of electricity, is thus proved; these phaenomena 

 being distinct from those of induction or molecular movements 

 taking place in the line of discharge, they are of a radiant 

 character, and due to the emission of tithonicity ; and we are 

 led at once to infer that the well-known changes brought 

 about by passing an electric spark through gaseous mixtures, 

 as when oxygen and hydrogen are combined into water, or 

 chlorine and hydrogen into muriatic acid, arise from a very 

 different cause than those condensations and percussions by 

 which they are often explained, a cause far more purely che- 

 mical in its kind. If chlorine and hydrogen can be made to 

 unite silently by an electric spark passing outside the vessel 

 which contains 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 dis- 

 charged, without chemical charges being brought about by 

 the radiant matter emitted. 



Proofs of the exactness of the indications of the Tithonometer. 

 — 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 

 advantageous to employ the following method of obtaining a 

 flame of suitable intensity. 



2 D 2 



