Sept 17. 1826 –
Your note of the 24th August <1> reached me just as I was on the point of leaving London and It is only now that I have a leisure hour to thank you for it & for your trouble in bringing poor Fraunhofer’s work & Professor Gruithuisen’s plates, <2> which I shall take care & send for on my return which will be very soon.– I wrote to you at Florence and have since received a letter from you dated Richmond <3> for which also I beg to thank you. What you say about Pons’s system of Comet Catching <4> & Amicis instruments, <5>
are is very curious.
I have been vulcano-hunting in Auvergne & have suffered great discomfort since in crossing the desolate tract of barren limestone that intervenes between Saint Flour in Cantal, and this place. At Issoire I went bone-grubbing and found some hyćna’s jaws and bits of shin bones, deer horns, tiger’s teeth &c. and saw with my eyes the tusk of an elephant (dug up about two months ago about a mile from the town), of which the fragments pieced together form a mass 8 feet long – 9 inches diameter at the thick end and 6 at the thin. Supply the wanting portions, & concieve the size of the beast! I wished to have got it for the Geological Society but it has fallen into the claws of the Mayor of Issoire, on whose estate it was found in digging a cellar, and who means to keep it all to himself. The accounts recieved in England of the gisement <6> of these extraordinary fossils is [sic] very erroneous. Buckland <7> has been examining them very carefully & will no doubt give an accurate description of them when he returns to England.
I am much disappointed in Montpellier, which I had figured in my mind as an earthly paradise – whereas it is a mere French country town in an uninteresting monotonous country without scenery & without a sea view. but I expect much from Nismes.– From this I shall direct my course homeward through the Vivarais, after visiting the Crater & lava-currents stated to exist at Agde a place a few miles South of Cette. I dare say you know this part of the world already. All I can say of it is that it is very hot, dusty, & disagreeable and that I shall be very glad to be out of it.
I carried up the Puy de Dome an instrument <8> for measuring directly the force of Solar Radiation by a new method, but the circumstances of weather were so unfavorable that I can determine nothing from my observations there – only the instrument answers fully my expectations, and speaks a language not to be misinterpreted. I think I have stated the principle to you in conversation – It consists in
measuring determining not, statically, any point of Equilibrium between the heating power of the Sun & the cooling causes in action – but, dynamically – the momentary increments of temperature due to the Suns rays plus those causes and to those causes alone. I believe the intensity of the Solar Rays may be hit very readily within a hundredth part of the whole, at any given moment, and place, by this method, and I have observations at different times & places, comparable inter se, <9> which shew how enormously greater the effect is on some days than on others, even when from the cloudless appearance of the heavens one would suppose it should be nearly the same.
But I am tiring you and I have other letters to write & so I must remain, in hopes of being fortunate enough to meet with you in Town this winter
Dear sir truly yours,
H.F. Talbot Esqr
31 Sackville Street
port de Montpellier pour Angleterre
2. Franz von Paul Guithuisen, Sechs Mondkarten (Bonn: 1821).
4. Jean Louis Pons (1761–1831), astronomer.
5. Prof Giovanni Battista Amici (1786–1868), Italian optician & man of science.
7. Probably William Buckland (1784–1856), geologist.
8. This was the ‘actinometer’, an instrument of Herschel’s own invention that measured the difference in the intensity of the sun’s heating rays. He described it fully in ‘Extract of a Letter to Dr Ritchie Explaining a New Process of Actinometry’, Edinburgh Journal of Science, v.3, 1825, p. 107.
9. In themselves.