Faraday to John Henry Vivian   18 February 1823

R Institution | Feby 18th

Dear Sir

I sent off the proof you speak of in the letter I have just received, two or three days since and hope you received it yesterday at latest¹[.]

The fact of the difference in the times of setting up dry and toughened copper is very curious but I am not quite sure I understand it. The one you say was much longer setting than the other but you have not said whether they were both at first of the same temperature[.] If they were as I suppose I presume the effect will depend upon the difference in the fusing points of the copper in these two states and which may readily be ascertained by experiment[.] It is curious and well worth insertion in your account.

I do not see any thing so curious in the other fact[.] It probably depends upon the scrap in the water forming a kind of envelope about the copper and which by the double effect of being a bad conductor of heat and also interfering & retarding the escape of the shower formed by the hot spray prevents the rapid abstraction of heat from it & preserves it hot for a longer time. I do not know whether the fact is practically useful or not if not I think it is hardly worth notice in the R.S. but those who see the effect are better judges that I am.

Your obedient Faithfull | M. Faraday

J.H. Vivian Esq | &c &c

Address: J.H. Vivian Esq | Truro | Cornwall