()2 Mis. No. 48. 



Of the three systems now in use for thermometric and barometric scales, 

 (the Reaumur and the French inch, the Fahrenheit and the English inch, 

 and the centigrade with the niinimetre,) that to which preference is gene-* 

 rally given on the continent of Europe, is the centigrade and the metric 

 system. Germany is gradually abandoning the Reaumur division and the 

 French inch for the centigrade and the millimetre. In some of its most 

 important scientific works, as the Meteorology of Kaemtz, several memoirs 

 of Dove, the Physical Atlas of Berghaus, and the accompanying text the 

 latter have been adopted. By degrees, Italy is doing the same, and we 

 shall soon have for choice only the Falyenheit and the Englisli inch on 

 one hand, and the centigrade and the millimetre'on the other. 



But to wliich of these two systems ought we to give tire preference? I 

 do not hesitate to say, to the second. It is the most rational and the most 

 convenient, it is that which has the greatest chance of uniting all suffrages 

 and of becoming universal. But it is reserved to America to settle this 

 question. Her weight in the balance will be decisive. If, renouncing the 

 system she has inherited from England, she adopts the centigrade and me- 

 tric scales, the scientific world may hope soon to arrive at that uniformity 

 in measures so desirable. England would not be able to hold out long 

 alone. 



It would be worthy of the Smithsonian Institution, which owes its origin 

 to a love of science transcending all spirit of nationality, to take here the 

 initiative, which its position, so perfectly independent, permits. The 

 adoption of these scales for the numerous instruments, which it intends to 

 spread over the whole surface of the United States, together with the 

 regular publication of observations under this form, will soon compel all 

 observers to conform to it. I am not ignorant of the objections which 

 might be urged against this measure, nor do I undervalue them. Never- 

 theless, I believe that I should be able to meet them, and I would do so in 

 advance, did I not fear to extend this communication beyond suitable lim- 

 its. 



The co-operation of Professor Bache would be of very great importance. 

 As superintendent of the coast survey, he has a number of publiqalions to 

 make on the temperature of the sea at different depths, for example, and 

 others, for which it would be useful to adopt the centigrade scale, or at 

 least to place the centigrade opposite to the Falirenheit degrees. This scien- 

 tific authority, joined to that of the Smithsonian Institution would, I doubt 

 not, be sufficient to introduce gradually so desirable a reform. The mo- 

 ment is critical — later, a change would be almost impossible. 



■^^ 4^ -l^ ^& -^ ^^ :^ ddfe ^K 



The importance which the subject of the change of scales seems to me to 

 possess, and the exigency of the moment, induce me to offer some further 

 considerations thereon, for which I crave your indulgence. 



Unif >rmity of notation in all scientific works is the essential and imme- 

 diate result at which we should aim. We might, strictly speaking, admit 

 any scale, provided it were universally adopted; but since, among the 

 number of those which have been proposed, there are three which have 

 divided the suffrages, it is from among these that we should select. Other 

 things being equal, two reasons (as 1 have already remarked) it seems to 

 me should determine our choice; the first is the relative perfection of the 

 scale; the second is the probability of its adoption by all men of science. 



As to the first point, the centigrade scale has the advantage over the 



