Cambridge | May, 6 ‘55.1
My dear Sir,
You were kind enough some time ago to say that you would undertake some experiments which I suggested on the conductive powers of certain compressed substances.2 I have had specimens formed of several substances, three of each under different pressures up to 12 or 14,000 lbs. on the square inch. My object is to ascertain the effect of these different pressures on the conductive power. I have wished you to undertake these experiments knowing that you have a delicate apparatus3 adapted for these, and conceiving also that you have established a sort of claim to add these new substances to those you have already experimented on, supposing you to have a wish to extend these researches. If therefore other engagements will allow you to undertake them, I again say how glad I shall be to place the experiments in your hands.
The specimens which have been formed for me of spermaceti,4 wax, tin, zinc, lead, clay &c are cylinders 4 or 5 inches long and a bar of about 3 inches diameter. From these I will have smaller specimens out of any form and size which may be most convenient to you if you will have the kindness to let me know what they shall be.
It is also of the first importance in certain geological speculations to ascertain the conductive powers of certain hard crystalline rocks as compared with those of mere earthy structure. Of these also I will have specimens formed for you should you undertake the experiments.
Believe me | Yours very truly | W. Hopkins.
RI MS JT/1/TYP/2/606
LT Typescript Only
May, 6 ‘55.: This letter was either dated incorrectly or reflects a typographical error. LT noted ’54?’ in the margin, which is probably correct. Hopkins wrote here that ‘some time ago’ he had requested Tyndall to undertake some experiments, which likely referred to experiments discussed in letters 0753 and 0862. See also letter 0938.
You were kind enough … certain compressed substances: not identified. Tyndall had presumably responded to letter 0753. See also letter 0862.
a delicate apparatus: see letter 0753, n. 5.
spermaceti: see letter 0753, n. 2.
Please cite as “Tyndall0929,” in Ɛpsilon: The John Tyndall Collection accessed on