[Illustration: Fig. 40.] “In conclusion, I beg to send you herewith a photograph of Philipp Reis (see Fig. 12, p. 23), holding in his hand the instrument I helped him to make, and which photograph he took of himself, exposing the camera by a pneumatic arrangement of his own, and which formed part of a little machine which he concocted for turning over the leaves of music-books. “The instrument used by Reis at the Physical Society may have been the square block form: I believe that this cone-form was not quite completed then. At the Saalbau (Hochstift), however, I am _sure_ the instrument shown in my photograph was employed; not with a tin cone, but a wooden one. I send you herewith a sketch of what I remember that instrument to have been. I am not absolutely certain whether in the instrument there was not an electromagnet introduced, but I think not. My recollection leads me to suppose that the electromagnet arrangement was added subsequently. Thinking it over again, I should, however, think that the instrument in the photo must have been one in which a bent lever was placed behind the tympanum, and that the rectangular patch seen above was a wooden casing to shelter the parts. There may be some confusion in my mind as to the position of this box, but I somehow think the rectangular patch is only part of a larger box which is not apparent in the photograph. I have no idea where the original instrument is now, but I should hardly think it could be in existence. Reis used to take some instruments to pieces to utilise parts in subsequent experiments, and I recollect how keen he used to be about the bits of platinum, which he always described as ‘ein sehr kostbares Metall.’ What always was a great puzzle was the attaching of the platinum plate to the membrane, which he did generally by sealing-wax, saying at the same time: ‘Es ist nicht recht so, aber ich weiss nicht wie es anders gemacht werden kann!’ “Believe me, my dear Sir, yours truly, “Ernest Horkheimer.” * * * * * Dr. Rudolph Messel. [The following letter from Dr. Rudolph Messel, F.C.S., addressed to the author of this book, in reply to enquiries concerning Reis and his inventions, speaks for itself. Dr. Messel’s letter differs from almost all the others here reprinted in having been specially written for the purpose of being inserted in this volume.--S. P. T.] “36, Mark Lane, London, _30th April, 1883_. “Dear Professor Thompson,