416 KEPORT — 1892. 



have botli made important contributions in this direction. In a paper • 

 read before the Royal Society by Professor Ewing the principles of 

 seismographic construction are unfolded. The author remarks that 

 the difficalty in earthquake measurements is to find a point which 

 does not move during the disturbance. The bob of a pendulum, if 

 suspended by a spiral spring, remains at rest vertically and horizontally, 

 especially if the pendulum be long and the frame to which it is suspended 

 rigid ; but there are two reasons why an instrument on this principle is 

 not efficient. In the first place, the recording portion is not easy to make 

 in a satisfactory manner; secondly, the motion of the point of suspension 

 causes a corresponding motion to be communicated to the bob, which, if 

 the period of earthquake oscillation agreed exactly with the pendulum's 

 free period, would altogether vitiate the result. He then describes a 

 seismograph devised by himself, in which solid cylindrical bobs are 

 pivoted with their axes vertical between steel centres. These centres 

 are carried by a frame, and attached to the frame is a style with a tracing- 

 point, so that when the frame is moved forward by a sudden earth-tremor 

 the inertia of the cylindrical bobs causes them to remain nearly, if not 

 quite, at rest. A plate or recording surface, which is connected with the 

 frame and moves with it, thus receives by means of the style a mark 

 corresponding in magnitude to the intensity of the earth-movement which 

 it is required to record. By placing the two frames carrying the bobs in 

 position at right angles to each other, the components of any horizontal 

 motion can be recorded. This instrument is called by the inventor the 

 ' Astatic Horizontal Lever Seismograph.' Since that time Professor Ewing 

 very much improved bis original idea, and reference to papers describing 

 the result will be found in the index of subjects appended to the report. 

 Professor Milne has also devised self-recording arrangements in connec- 

 tion with earthquakes, many records obtained by which, in the grounds 

 of the Tokio Engineering College, having been described by him.^ 



Similar instruments have been used by Professor Milne ^ for studying 

 the motion of locomotives, in which both the vertical and the horizontal 

 motion is recorded, the continuous record being obtained on a band of 

 paper, as on the Gray-Milne seismograph. The authors mention the 

 following types of instruments : — 



1. ' For timing trains, and giving general information respecting the 

 condition of a line. This consists of the double-clock arrangement just 

 described, driving a continuous band of paper about 2^ inches broad at 

 the rate of 1 foot per hour. On this band only the vertical motion is 

 written ; but inasmuch as lateral jei'ks have usually a vertical component, 

 these also are in part recorded. 



2, ' For giving detailed information respecting a line. In this instru- 

 ment clocks similar to those of No. 1 are employed, but the band of 

 paper driven by them is broader, and all the components of the motion 

 are recorded upon it. In addition to timing a train and showing irregu- 

 larities on the line, this instrument indicates curves and gradients, shows 

 when brakes are applied, &c. 



' 'On a New Seismograph,' by J. A. Ewing, B.Sc. Proceedings of the Eoyal 

 Society, No. 210, 1881. 



'-' ' Construotion in Earthquake Countries,' by J. Milne. Min. Proc. Inst. C.E., vol. liii. 



•'' ' On the Vibratory Movements of Locomotives, and on Timing Trains and Test- 

 ing Railway Tracks,' by J.W.Milne, F.R.S., and John MacDonald. Min.Proc. Inst.C.E., 

 vol. ciii. 



