The ‘father’ of modern seismology (1850–1913) credited with developing the continuous recording seismograph. Scarce ALS, four pages on two adjoining sheets, 4.25 x 7, Shide Hill House letterhead, September 20, 1897. Letter to a professor, including a fascinating sketched diagram of a proposed experiment. In part: “I wish to determine the radius at which mechanical vibrations are actually transmitted through various materials, which I fancy are less than vibrations deduced from elastic moduli. Is it likely that results of any value would be obtained from the following experiment: [Diagram]. AB is a bar of material. When struck by pendulum P1, after a short interval P2 will fly off from A. As shown, an electric circuit open at B and the armature at M is not in contact with its magnet. When P1 comes in contact with B the circuit is closed and the armature is moved and it again moves when P2 rebounds from A. If AB is first very short to get the time of making & breaking circuit and the interval subtracted from the time interval obtained when AB is a few feet in length should give the time taken by a wave to pass from B to A. If AB was of steel & 1 meter in length the time taken for a wave of compression will be less than 1/6000 second. Is this likely to be less than the time taken for the make and break of a magnet actuating a very light needle like armature writing on a revolving disc of glass coated with smoke? If such experiments have not been made would you kindly advise me how to best form a magnet & high speed chronograph? The velocities I have to deal with first now are through the crust of the interior of the earth…& I want speeds through various materials when hot & cold etc. for purpose of comparison.” A uniform shade of toning, light paper loss to upper left corner, and brushing to the signature, otherwise fine condition. An interesting letter from one of the most important figures of early seismology. RRAuction COA.
