354 L IFE AT DOWN. /ETAT. 33-45. [1847. 



shorter intervals. Most people, I suspect, who like myself 

 have dials, will wish to be more precise k than with a margin 

 of three minutes. I always buy a shilling almanack for this 

 sole end. By the way, yours, i,e. Van Voorst's Almanack, is 

 very dear; it ought, at least, to be advertised post-free for 

 the shilling. Do you not think a table (not rules) of conver- 

 sion of French into English measures, and perhaps weights, 

 would be exceedingly useful ; also centigrade into Fahren- 

 heit, magnifying powers according to focal distances? in 

 fact you might make it the most useful publication of the age. 

 I know what I should like best of all, namely, current meteo- 

 rological remarks for each month, with statement of average 

 course of winds and prediction of weather, in accordance 

 with movements of barometer. People, I think, are always 

 amused at knowing the extremes and means of temperature 

 for corresponding times in other years. 



I hope you will go on with it another year. With many 



thanks, my dear Jenyns, 



Yours very truly, 



CHARLES DARWIN. 



C. Darwin to J. D. Hooker. 



Down, Sunday [April i8th, 1847]. 



MY DEAR HOOKER, I return with many thanks Watson's 

 letter, which I have had copied. It is a capital one, and I am 

 extremely obliged to you for obtaining me such valuable 

 information. Surely he is rather in a hurry when he says 

 intermediate varieties must almost be necessarily rare, other- 

 .wise they would be taken as the types of the species ; for he 

 overlooks numerical frequency as an element. Surely if A, B, C 

 were three varieties, and if A were a good deal the commonest 

 (therefore, also, first known), it would be taken as the type, 

 without regarding whether B was quite intermediate or not, 

 or whether it was rare or not. What capital essays W. 

 would write ; but I suppose he has written a good deal in the 



