426 Dr. Stenhouse on Thcine and its Preparation. 



produce similar effects, and certainly I have established the 

 necessity of examining all the phaenomena with great care and 

 attention, before we attempt to establish a theory which shall 

 embrace the whole class. I have given the name Thermo- 

 graphy to these images, under a conviction that heat was most 

 importantly engaged in producing them, and I see no reason 

 for altering the name. At the same time I beg to be very di- 

 stinctly understood, that I am not wedded to this opinion ; I 

 feel conscious that we are dealing with some of the most sub- 

 tile agents in nature, and that we cannot too jealously guard 

 against the deceptions of the senses. That which heat appears 

 to produce, may be the creation of some other element, which 

 is excited only by calorific influence. But although I hold 

 my judgement under suspense, particularly when I find light, 

 heat, electricity, chemical action and mechanical force, all 

 producing the same effects, I cannot at present entertain the 

 idea of " invisible light," although M. Moser states, that in his 

 memoir on Vision, he has demonstrated its existence. In con- 

 clusion, I must hope that I have been successful in proving that 

 I have not in this instance, or in any other, endeavoured to 

 appropriate the experiments of another. I have ever stu- 

 diously endeavoured to give the merits of even the slightest 

 suggestion to its author, and if in any one instance, in the case 

 of Professor Moser, I have not done so, I have erred through 

 ignorance, and not by design. I cannot, however, detect any 

 grounds for M. Moser's attack. I commenced my first paper 

 with a statement of his results, and I concluded it by giving 

 my opinion on the importance of the discoveries he had made. 

 I cannot, however, allow myself to be led away from that 

 which appears to me to be the legitimate path of inquiry by 

 any unkind feeling. I shall pursue the investigation, and the 

 moment I can convince myself that light is engaged in these 

 phaenomena in darkness, I will acknowledge the correctness 

 of Professor Moser's views with heartfelt pleasure. 

 Falmouth, November 4, 1843. Robert Hunt. 



LI. On Theine and its Preparation. By John Stenhouse, 

 Esq., Ph.D.* 



r | 1 HE process which I have found most suitable for preparing 

 ■■■ theine, is both easy and productive, and is simply as fol- 

 lows : — A decoction of tea is first treated with a slight excess 

 of acetate of lead, which throws down the tannin, and almost 



• Communicated by the Chemical Society, having been read March 21 

 and May 2, 1843. 



