Most heartily do I thank thee oh! Heinrich for thy instructive letters to me.2 Please thank Flight3 for me for that useful calculation.
No doubt a good deal of aqueous vapour would be mixed up with the scent of the onion.4 I experimented thus. I passed air first over the onion, and then over fragments of potato cut in a similar manner. I deducted the offset of the potato from the total effect of the onion, and in doing so I assumed that I deducted the aqueous vapour.
Could you not apply the same method? At all events you can do this—As far as aqueous vapour is concerned the large Spanish onion and the small common onion will act alike, but as far as the odours are concerned the small common one is very much stronger than the Spanish are. Could you not send air over both, and see whether they lost alike or lost differently: if differently the balance wd be due to odour of the common onion, if sensibly alike it would shew that the quantity of matter producing this odour must be very small. My object is to get some idea of the quantity of matter which produces the effects that I have observed.
Would not this be a good experiment! Musk you say has been thought to give its scent to a process of decay due to oxidation. Suppose I make pure hydrogen the vehicle for conveying the scent into the tube if the scent be due to oxidation I ought to get no action if it be independent of oxidation I ought to obtain the same effect with hydrogen as with air—This experiment it appears to me would decide whether the scent was due to oxidation or not.
Thank you very much for your offer of the liquids5—I will seek what Frankland Williamson6 & Hoffmann7 can give me, and if they have not all I require I will write to you.
Our atmosphere hardly stops radiant heat at all. It is sensibly a vacuum, and those observations from which the opacity of the air has been inferred are entirely due to the extraneous matters in the atmosphere & mainly to the aqueous vapour.
The aqueous vapour on the 10th of this month exerted an action at least 40 times that of the whole air.8
During last full moon I experimented on her radiation and found my thermo-electric pile when turned on the moon lost more heat than when turned on any other part of the heaven of the same altitude. It was practically a radiation of cold. I have written a short letter to Herschel on these subjects which will appear in the next Phil. Mag.9
goodbye Heins | Yours ever | John Tyndall
Alternierende Ströme10 are, I should say, what you obtain by induction in making and breaking contact—they are in opposite directions.
RI MS JT/1/TYP/7/2369–2370
[Late October 1861]: the letter refers to Tyndall’s moon experiments which were carried out on 18 October and follows a letter sent to Debus on 24 October (see letter 1817). A later letter followed in early November (see letter 1823).
thy instructive letters to me: letters missing.
Flight: Walter Flight (1841–1885), mineralogist taught by Tyndall and Debus at Queenwood (ODNB).
scent of the onion: see letter 1817.
Your offer of liquids: Tyndall has asked Debus for some volatile liquids in a previous letter (see letter 1787).
Williamson: Alexander William Williamson (1824–1904), British chemist (ODNB).
Hoffman: August Wilhelm von Hofmann (1818–92), German organic chemist.
an action at least 40 times that of the whole air: on 10 October 1861 Tyndall noted in his laboratory notebook: ‘it is certain that the foreign contaminants in the air of the laboratory exert at least 67 times the absorptive power of the air itself, and the aqueous vapour alone exerts about 40 times the absorption of the air’. Experimental Diary, 10 October 1861, RI MS JT/3/46.
in the next Phil. Mag: John Tyndall, ‘Remarks on radiation and absorption,’ Phil. Mag., 22 (1861), pp. 377–8.
Alternierende Ströme: alternating current.
Please cite as “Tyndall1820,” in Ɛpsilon: The John Tyndall Collection accessed on