Mr. Hunt on the Spectral Images q/M. Moser. 415 



The same original volume of gas in a d will last for a long 

 time, as we keep replenishing it as often as the fiftieth division 

 is reached. 



The experimenter cannot help remarking, that on suddenly 

 exposing the sentient tube to a bright light, the liquid for an 

 instant rises on the scale, and on dropping the cap in an in- 

 stant falls. This important phasnomenon, which is strikingly 

 seen under the action of an electric spark, I shall consider 

 hereafter. 



In conclusion, as to comparing the tithonometric indication 

 at different times, if the gases have the same constitution, the 

 observations will compare ; and if they have not the value can 

 from time to time be ascertained by exposure to a lamp of con- 

 stant intensity. To this method I commonly resort. 



From the space occupied in this description the reader 

 might be disposed to infer that the tithonometer is a very 

 complicated instrument and difficult to use. He would form, 

 however, an erroneous opinion. The preliminary adjustment 

 can be made in five minutes, and with it an extensive series of 

 measures obtained. These long details have been entered into 

 that the theory of the instrument may be known, and optical 

 artists construct it without difficulty. Though surprisingly 

 sensitive to the action of the indigo ray, it is as manageable by 

 a careful experimenter as a common differential thermometer. 



University of New York, Sept. 26, 1843. 



L. On the Spectral Images of M. Moser; a Reply to his 

 Animadversions, Sj-c. By Robert Hunt, Secretary to the 

 Royal Cornwall Polytechnic Society *. 

 To U. Taylor, Esq. 

 Dear Sir, 

 [ CANNOT but regret that any remarks which I may have 

 made on the very interesting discoveries of Professor Moser, 

 should have so far disturbed the philosophic quiet of his mind, 

 which it is so important to maintain, when engaged in the in- 

 vestigation of truth, as my paper on Thermographyf appears 

 to have done. I am, however, called upon to reply to M. 

 Moser's remarks, which appear in your Journal for Novem- 

 ber, in a way that is very unpleasing to me. However much 

 men may differ in the interpretations they give to obscure 

 phaenomena, I do not fancy they will approach any nearer the 

 truth, or facilitate the progress of inquiry, by indulging in 

 personal attacks. 1 have ever pursued my inquiries with, I 

 hope, but one object in view. The investigation of curious 

 phaenomena has ever been a pleasure to me, and an occasional 

 discovery has been its own exceeding great reward. I never 

 * Communicated by the Author. f Phil. Mag., Dec. 1842. 



