Cambridge | April 24 ’58
My dear Sir,
A great current has always been described by Rennell1 and others (as I have understood) as originating in the Indian Ocean and usually attributed to the trade winds. It runs south westerly along the S.E. coast of Africa, doubles the Cape takes a N. Westerly course and then a more westerly one along the Equator (where it known as the Equational current) to the coast of Brazil and the Caribbean Sea. It seems there to be in some degree lost as a distinct current, but I have never doubted but that there must be a movement in that sea which supplies the water poured out from the Gulf of Mexico as the proper Gulf stream continuing its course N. Easterly to our own shores. Hence it is that I have spoken of the Gulf stream as being reflected from the coasts of America.
I trust we shall ere long know more about ocean currents than we do at present. I have never speculated on the causes of them and in fact have been disposed to avoid doing so on account of our imperfect knowledge of the facts. I have always regarded the trade winds a vera causa2 of currents but have thought little as to other causes which may exist. I have not considered with any care the cause you mention,3 but supposing it to produce an easterly current in the northern Atlantic, how shall we account for the westerly currents to the South of the Cape of Good Hope and Cape Horn, both of which I imagine are ascertained beyond doubt. However if you pursue the subject I shall be glad to hear your speculations upon it.4
Yours truly | (in haste) | W. Hopkins.
RI MS JT/1/TYP/2/614
LT Typescript Only
Rennell: James Rennell (1742–1830), an English cartographer and historian who studied the currents of the Atlantic and Indian oceans (ODNB).
vera causa: a true cause (OED).
the cause you mention: not identified (presumably in a letter from Tyndall to Hopkins that is missing).
if you pursue the subject I shall be glad to hear your speculations upon it: at the time of this letter, Tyndall was about to give the last of the three extended lectures on heat (April 29, see letter 1510, n. 9). He was interested in heat as it related to wind and ocean currents, as this reply to a missing letter to Hopkins presumably shows. In Tyndall’s published 1862 heat lectures, Heat as a Mode of Motion (London: Longman, Green, Longman, Roberts & Green, 1863), he discussed wind and ocean currents in chapter 6 (pp. 167–93).
Please cite as “Tyndall1513,” in Ɛpsilon: The John Tyndall Collection accessed on