To Thomas Archer Hirst   25th. Feb. 1853

Queenwood | 25th. Feb. 1853.

My dear Tom

The image¹ of you sitting on the ice with a star beneath your stern-works convulsed all my frame with laughter. I suppose by this time you will have received my short account of the proceedings in London.² Nothing definite is settled yet. It is likely that two openings will occur one at the Royal Institution one at the London Institution. But as yet I have had no definite offer. I am to give four lectures at the Royal Institution in May and June,³ and a lecture on the 16th of March at the London Institution.⁴ I am so much occupied that I have but little time to prepare and I want you to assist me a little. I want a few notes regarding the difference of temperature between day and night in the desert of Sahara and also the difference between day and night in some forest regions in the same latitude as the desert. My object is to compare the influence of silica with that of [regation] upon climate. Now nobody can give such information better than Professor Dove and nobody I think will give it more readily. If he is acquainted with any peculiarities of the desert as regards temperature I should be thankful to be informed of them. The fact is quartz or pure silica, the prevalent mineral in Sahara is a better conductor of heat than many of the metals and this peculiarity must I think have great influence upon the climate of the desert. I imagine à priori that a maximum and minimum thermometer ought to shew a far wider range of temperature in the 24 hours in the desert than in a wooded region in the same latitude. Ask Prof. Dove does he not think so. Now I want you to send me this information immediately. I send you a cheque for 20 pounds as I shall want to draw upon you to pay for some crystals which I am getting out in Frankfort.⁵

Your affectionate | John

RI MS JT/1/T/560

RI MS JT/1/HTYP/229