From Alexander Herschel   1863 Mar 15th

Collingwood | Hawkhurst | 1863 Mar 15^th

Dear Sir

My father¹ was good enough to give me your kind message² offering the use of any apparatus which you could furnish for the illustration of my lecture on shooting stars and Fireballs at the Royal Institution on the 24^th April.³ Can I have the use at that time of a Ruhmkorff coil⁴ and one or more large vacuum tubes either of the direct discharge construction or the inductive discharge construction? The last contrivance which shews the current in many different gases in successive cells is very beautiful but I am anxious to shew the action of a magnet upon a luminous current in causing it to deviate or be bodily transported to one side. In your lectures on heat⁵ I see the great power of originating a current, which a magnet possesses, in a moving conductor, beautifully exemplified and illustrated by a pyramidal reflector (crowning a revolving piece of silver). If a passing current moves a needle, and a moving needle passes a current, but backwards, and in the opposite direction, I suppose that when motion of a needle underneath a galvanic current is permitted, a loss of power is occasioned in the electric current proportional to the effect produced. The same would happen if the current were moveable and the needle fixed. Would not then a mobile or transportable current such as the luminous currents through rarefied air become not only locomotive but also vacillatory or fitful in intensity in proportion to their mere irregular mobility, in presence of a strong magnet? A steady source of electricity and steady magnetism might thus cause the fickle beams of auroral displays by the different characters of the volumes of air successively subjected to the discharge in the sidelong progress of the current? When most stationary the discharge would be brightest.

In alluding to auroras I wish to throw a beam of light upon a basin of water to represent the ‘merry dancers’ or quickest and most locomotive flashes, with some fidelity, by reflection upon the ceiling. I think by proper treatment of the basin the truth may be pretty fairly imitated.

I remain dear Sir | yours most sincerely | Alex[ande]^r S. Herschel.

RI MS JT/1/H/82

RI MS JT/1/TYP/2/583