Faraday to Edward Vivian   14 September 1853¹

Royal Institution | 14 Septr. 1853

My dear Sir

I feel it very difficult to give an opinion on your case not having the opportunity of seeing the instruments so as to judge of how they were constructed and at the same time of asking questions of you or the maker: I will not restrain myself however from making suggestions but remember I do so with insufficient data[.]

I do not see how the mere difference in size of the air spaces a & b can cause the change you mention especially as you say the alteration comes to an end after a certain time as six months[.] Is not the cause a real difference in the character of the atmosphere in the two air spaces? and is not the gradual change a consequence of the slow equilibration of these different atmosphere by their gradual transmission through the separating column of spirit? the effect going on until they are alike & then ceasing. I observe that the bulbs a.a.a. in which the air expands are all of them those which are last finished in the construction of the instrument and it seems to me that when the bulbs were finally sealed the air within them mingled as it would be with alcohol vapour has been affected & changed in part by the heat applied. Hot glass in a mixed atmosphere of air & alcohol vapour will form carbonic acid, acetic acid, & other products & in this way the air a may at the first be diffused to the air b. If for instance by any such change the air a is partly deprived of a portion of its oxygen then oxygen will slowly pass from b to a until both are alike again[.]

I only suggest this change in the oxygen & this kind of change by heat as illustrating the kind of difference which I suspect exists in the new instrument. The difference may be caused some other way. For instance the air may be introduced by some particular process - the mouth or lungs may be used or other means & in these the cause of the first difference may be[.] I have not even the means of guessing not knowing the particular method of construction pursued by the maker but I think you will find a difference of this kind at the root of the matter[.]

Before concluding let me ask why you say the difficulty is insuperable? The instruments at last come to a settled condition & if you do not graduate until then I suppose all would be right.

I am very pleased to renew our acquaintance in any manner and am

My dear Sir | Very Truly Yours | M. Faraday

Edwd Vivian Esq | &c &c &c

Will the following point help you. Glass which has been heated is said to return to its final volume when cooled only very slowly and after some weeks or months. I think Bellini² in this way accounted partly for certain changes in thermometers which went on even for years³. Can any such effect occur with you | MF