S40 On t?ie Hygrometer. 



point to be the same, and the circulation of air equally rapid, 

 the rate of evaporation in the former case to that in the latter 

 would be as f^ — f^, to f^ — f^,. Perhaps, therefore, the inten- 

 sity of evaporation has been found to be as f^ — j^,, from the 

 depth of water generally used in making the experiments having 

 been sufficient to preserve the temperature nearly at t Or, it may 

 be, that the difference of temperature t — t', by increasing the cir- 

 culation of air over the colder surface, compensates for the smaller 

 quantity of moisture which each portion of air contains, and 

 thereby renders f^ — f^, the true measure of the quantity eva- 

 porated in both cases. However, from the result of one expe- 

 riment, in which two moist surfaces were exposed, one in the 

 sunshine, and the other in the shade, the writer is led to think, 

 that the temperature of the evaporating surface affects the pro- 



Marine Insects destroyers of Wood. 



My dear Sir, Leith, Ut August 1834. 



In my paper on the Limnoria terebrans, published in the Edin- 

 burgh Philosophical Journal for April last, I stated that the ravages 

 of that animal were first noticed at the Bell-Rock, by Mr Stevenson 

 in 1809 : and this, I believe, has been the general understanding 

 among zoologists for many years past. But I find, in the twenty- 

 second volume of the Journal de Physique (1783), an account by the 

 Abbe Dicquemare, of the destructive effects produced at Havre by 

 the agency of a minute crustaceous animal, which, from the descrip- 

 tion and figures given by the author, I have no doubt was of the 

 same species as that now called Limnoria terebrans- It is only with 

 the view of adding something to our acquaintance with the history of 

 an animal which is so interesting to us on account of the peculiarly 

 destructive effects of its habits, that I now direct your attention to 

 the paper by Dicquemare, above referred to. I enclose a translation 

 of part of it, which you will oblige me by inserting in the next num- 

 ber of your Journal, as a correction of the misstatement contained in 

 the account of the structure and habits of the Limnoria formerly pub- 

 lished. I am, my Dear Sir, yours most faithfully, 



John Coldstream. 



To Professor Jameson. 



