57° 



SCIENTIFIC NEWS. 



[June 15, i£ 



direction with such rapidity that a point on the earth's 

 surface wriggled through a path like the form a loose 

 coil of string might taKe if it were ravelled into a state of 

 the utmost confusion. The mechanical problem in seis- 

 mometry was to find a steady point, to suspend a body so 

 that some point in it, at least, should not move while this 

 complicated wriggling was going on ; the steady point 

 would then serve as a datum with respect to which the 

 movement of the ground might be recorded and 

 measured. The simple pendulum had often been 

 suggested as a steadj' - point seismometer, but in 

 the protracted series of oscillations which made up 

 an earthquake the bob of a pendulum might, and 

 often did, acquire so much oscillation that, far from 

 remaining steady, it moved more than the ground itself. 

 This was on account of its stability. To prevent the 

 independent oscillation of the body whose inertia was to 

 furnish a steady point, it was essential that the body 

 should be suspended or supported astaticallj' — in other 

 words, so that its equilibrium would be very nearlj' 

 neutral. Methods of astatic suspension for horizontal and 

 vertical motion were described and illustrated by diagrams 

 and models. The complete analysis of the ground's 

 motion was effecte'3 by a seismograph, which resolved it 

 into two horizontal and one vertical component, and 

 recorded each of these separately, with respect to an 

 appropriate steady point, by means of a multiplying 

 index, on a sheet of smoked glass which was caused to 

 revolve at a uniform rate by clockwork. The clock was 

 started by the action of the first tremors of the earthquake 

 on a very sensitive electric seismoscope. The record 

 drawn on the plate gave every possible particular regard- 

 ing the nature of the motion at the station where the 

 seismograph was placed. A complete set of the appa- 

 ratus, as made by the Cambridge Scientific Instrument 

 Company, was shown in action. Professor Evving also 

 described and showed his duplex pendulum seismograph, 

 which drew upon a fixed plate of smoked glass a magni- 

 fied picture of the horizontal motion during an earth- 

 quake. Apparatus was shown for testing the accuracy of 

 the instruments by means of imitation earthquakes which 

 shook the stand of the seismograph and drew two 

 diagrams side bj' side, one the seismograph's record and 

 the other a true autograph of the motion of the stand. 

 This test was applied to the instrument on the table, and 

 the close agreement of the diagrams was shown by project- 

 ing them on the lantern screen. A number of autographic 

 records of Japanese earthquakes were thrown on the 

 screen, and their principal features were described. 

 Some of these had been taken since the lecturer left Japan, 

 by Mr. Sekiya, Professor of Seismology in the Imperial 

 University, who had also constructed a model (shown by 

 means of the lantern) to exhibit in solid form the 

 tortuous path through which a point on the earth's 

 surface moved during an earthquake. In general the 

 motion began with small tremors of high frequency, which 

 were probably transmitted by normal vibrations of the 

 crust ; these died out at an early stage in the disturbance, 

 but usually not until transverse motions of larger ampli- 

 tude and longer period had begun. The whole went on 

 with irregular fluctuations and with a protracted and 

 very gradual dying out of the shaking for two or three, 

 sometimes even for ten minutes, and comprised some 

 hundreds of movements to and fro and round fantastic 

 loops. As a rule, the horizontal movement was much 

 larger than the vertical. Each single movement usually 

 occupied from half a second to two seconds. Earthquakes 



were quite perceptible in which the greatest extent of 

 motion was no more than one-hundredth of an inch. In 

 one case, on the other hand, as much as an inch and 

 three-quarters had been registered. Even that was in an 

 earthquake which did little damage, and there was, there- 

 fore, reason to expect that a severely destructive shock 

 (such as had not occurred in Tokio since the present 

 system of seismometry was developed) would show still 

 more motion, perhaps much more. Professor Ewing con- 

 cluded his lecture by exhibiting seismographic records he 

 had recently taken on the new Tay Bridge to examine 

 the shaking of the bridge during the passage of trains. 

 The instrument had been placed on the southmost of the 

 great girders, where it was expected that the vibration 

 would be a maximum. The records showed that the 

 greatest horizontal motion never e.xceeded one-eighth of 

 an inch, even when a train was passing the seismograph — 

 a fact which spoke well for the stiffness of the structure. 

 Nevertheless, by watching the seismograph, one could see 

 the index begin to oscillate whenever a train came on at 

 the Dundee end of the bridge, a distance of one and one- 

 third mile from where the instrument was standing. 

 The movement began with longitudinal oscillations 

 through something like one five-hundredth of an inch. 

 When the train came a good deal nearer transverse 

 oscillations also were recorded ; and the bridge did not 

 cease to shake till the train had passed off at the other 

 end. 



ROYAL MICROSCOPICAL SOCIETY. 

 At the meeting held on May 9th, Dr. C. T. Hudson, 

 President, in the chair, Mr. Crisp exhibited a form of 

 camera lucida by M. Dumaige, of Paris, fitted in a box 

 with a cover, which, when closed, kept the prism and 

 mirror free from dust. Also, by the same maker, an 

 adapter with spiral springs, for rapidly changing objec- 

 tives, and a portable microscope, in which the foot and 

 stage were in one piece. Dr. Kibbler exhibited and de- 

 scribed a new stand and camera which, he believed, 

 would be found very useful for photomicrography. It 

 had been made to his design by Mr. Bailey, his idea 

 bemg that it was best not to take negatives upon a large 

 plate but on a quarter-plate first, and afterwards to en 

 large the pictures from the original negatives. The great 

 advantage of this method was in the amount of light 

 gained for the purpose of focussing. The quarter-plate 

 size was also the proper one for lantern slides. The 

 ordinary diaphragm-plate placed immediately below the 

 stage he had found entirely useless, but that by removing 

 it a certain distance from the object it then ceased to cut 

 oft' the field, and began to reduce the light and to improve 

 the penetration and definition. With high powers this 

 answered very well, but it would not work with low 

 powers, unless^the diaphragm was removed to a distance 

 too great to be convenient in practice. He had therefore 

 devised the plan of introducing a short i-^-inch condenser 

 behind the stage, and about three inches in front of the 

 diaphragm-plate, in this way throwing it out of focus. 

 The effect of this was that the same improvement in 

 penetration and definition was obtained, but on a much 

 shorter distance. Attention was also called to a method 

 of clamping the object in position when the focus had been 

 obtained ; also to a plan for obtaining a fine adjustment 

 by a tangent screw. Mr. Mills's note on " A Sponge with 

 Stelliform Spicules" was read. Mr. Crisp -referred to 

 some comments which had recently been made in America 

 upon the advantages of the method of.tilting the stage of 



