248 THE POPULAR SCIENCE MONTHLY. 



and only two copies of the edition existed in the middle of the 

 eighteenth century. But one of these copies was complete. It 

 belonged to the great library of the king. It was, however, re- 

 printed in 1777 by Gobet, who also reprinted, about the same time, 

 the works of Bernard Palissy. After the essays, Gobet published 

 a part of Key's correspondence with Pere Mersenne relative to 

 them, and there are probably still other letters in the manuscript 

 correspondence of Pere Mersenne. Key's book was therefore well 

 published at the close of the eighteenth century. Nevertheless, 

 this edition, too, is now very rare, and only three copies exist in 

 the libraries of France. 



As very few persons of this age have read the Essays of Jean 

 Key, we have thought it might be of service and cast some light 

 on the history of science, obscure in its beginnings, to give a brief 

 but exact analysis of its contents. Judging by his writings, Jean 

 Key appears to have had very extended scientific knowledge and a 

 talent for experimentation rare in his time. He was, furthermore, 

 in pleasant relations with most of the learned men of the period, 

 who were accustomed to consult him in difficult cases, while he 

 was correctly informed of all that had been done in France and 

 other countries. Three men in particular were closely associated 

 with his works viz., the Sieur Brun, master apothecary of Ber- 

 gerac ; Deschamps, a physician of the same city ; and Pere Mer- 

 senne, of the order of the Minims, who had a continuous and in- 

 teresting correspondence with him. 



Key's experiments were undertaken at Brun's request. Brun's 

 letter, giving as it does an idea of the confidence which Key in- 

 spired among his contemporaries and of his high reputation, 

 merits publication entire. He wrote : " Desiring a few days ago 

 to calcine some tin, I weighed two pounds and six ounces of the 

 finest English metal, put it in an iron kettle on an open furnace, 

 and, stirring it continually without making any change in the 

 adjustment, I converted it in six hours into a very white earth. 

 I weighed it to determine the loss, and found that it weighed two 

 pounds and thirteen ounces. This astonished me incredibly, for 

 I could not imagine where the surplus seven ounces had come 

 from. I performed the same experiment with lead, and calcined 

 six pounds. I found it had gained six ounces. I asked the cause 

 of this from many learned men, particularly from Dr. N. (Des- 

 champs), but none of them could explain it to me. Your brilliant 

 mind, which soars, when it is so disposed, above the common, will 

 find matter to occupy itself with in this. I implore you with all 

 my aft'ection to employ yourself with the search for the cause of 

 so rare an effect, and to oblige me so much that by your aid I may 

 be enlightened respecting this wonder." 



Key immediately set himself to work to find the answer to this 



