152 



NA TURE 



[June 12, 1884 



by three wires from a rigid tower, has done good work in 

 the writer's observatory, but such an instrument has obvious 

 drawbacks. Fig. 4 shows an arrangement, also used by 

 the writer, and called a "duplex pendulum." A common 

 pendulum with a ring bob, B,, is connected to an inverted 

 pendulum, B.„ by a ball-and-tube joint, which compels the 

 bobs to move horizontally together. The combination 

 can be made as nearly astatic as may be desired by pro- 

 portioning the masses of the bobs to the lengths of the 

 suspension-rods. The inverted pendulum stands on a 

 joint which gives two freedoms to rotate but prevents 

 twisting about a vertical axis ; an extension of its rod 

 upwards forms the multiplying arm, and carries a tracing 

 pointer. 



Another plan is shown in Fig. 5, which may be de- 

 scribed as a duplex pendulum with a single bob, whose 

 weight is borne partly by a socket below and partly by a 

 spring from a support above. Any one of these instru- 

 ments affords a single steady-point with respect to all 

 motions in azimuth. Their principal use is to give 

 " static " records of the horizontal motion, that is, records 

 traced on fixed plates, which show at a glance the changes 

 in direction of displacement during the occurrence of an 

 earthquake. 



In attempting to register the vertical component of 

 earthquake motions, we meet with the difficulty that the 

 weight of the mass whose inertia is to furnish a steady- 

 point acts in the direction in which freedom of motion is 

 to be retained. A weight hung by a spiral spring from a 

 support above it is too stable to act as a seismometer, 

 unless the spring be impracticably long. A horizontal bar 

 fixed to a wall by a flexible joint and loaded at its end — 

 an old device used by the British Association Committee 

 at Comrie in 1842 — is open to the same objection. If the 

 loaded bar is rigid, but pivoted about a fixed horizontal 

 axis, and held up by a spiral spring near the axis of sup- 

 port, we obtain a much slower period of free oscillation 

 than if the spring were directly loaded with a weight 

 which would stretch it to the same extent. Mr. Gray has 

 rendered this device as nearly astatic as may be desired 

 by adding a small tube containing mercury, whose effect 

 is to increase the load when the bar goes down and to 

 decrease it when the bar goes up. Another and simpler 

 way of attaining the same result is shown in Fig. 6, which 

 represents the vertical seismograph used in Japan by the 

 present writer. There a is a horizontal bar pivoted about a 

 horizontal axis on two points at c, with a heavy bob, b, 

 whose weight is borne by a pair of springs, d. But the 

 upward pull of the springs, instead of being applied to the 

 bar in the line joining the axis c with the centre of gravity, 

 is applied below that line by means of the stirrups. Con- 

 sequently, if the bar goes down, the pull of the springs, 

 although increased above its normal value, is applied 

 nearer to the axis, and (by properly adjusting the depth 

 ofc below the bar) the moment of the pull of the springs 

 may thus be kept as nearly equal to the moment of the 

 weight as may be desired — a condition which of course 

 secures astaticism. The centre of percussion of the 

 loaded bar is the steady-point, with respect to which the 

 vertical motions of the ground are recorded by the multi- 

 plying lever / on the rim of a revolving glass plate, o, 

 which may be the same plate as that which receives the 

 record of the two horizontal components. 



The instruments which have been briefly described 

 succeed in registering very completely all the movements 

 of the ground at an observing station during the occur- 

 rence of an ordinary earthquake, and some of them could 

 be adapted with little difficulty to the registration of 

 violent convulsions. It would be outside the scope of 

 this paper to deal with the appliances by which Rossi and 

 others have investigated those minute and almost in- 

 cessant tremors of the soil whose very existence no obser- 

 vations less fine and careful would serve to detect. 



J. A. Ewing 



NOTES 



The meeting for organisation of the American Association for 

 the Advancement of Science will be held on Thursday morning, 

 September 4 ; and on Friday evening, September 5, after the 

 address of the retiring President (Prof. Charles A. Young, of 

 the College of New Jersey), a general reception will be tendered 

 by the citizens and ladies of Philadelphia to the members of the 

 British and American Associations, and the ladies accompanying 

 them. The British Association has been cordially invited, both 

 by the American Association, to take part in their proceedings, 

 and hy the Local Committee representing citizens of Philadelphia, 

 to accept the warm welcome which will be tendered them during 

 the joint session. The Local Committee for the Philadelphia 

 meeting is divided into a number of sub-committees, which have 

 been specially created to render the stay of their visitors agree- 

 able. It is earnestly requested that every one who intends to 

 participate in this meeting will send his name, together with the 

 number of ladies and gentlemen in his party, at as early a date 

 as possible, to Dr. Persifor Frazer, Secretary of the Committee 

 on Invitations and Receptions, 201, South Fifth Street, Phila- 

 delphia. During the week occupied by the session a number of 

 receptions, entertainments, and excursions will be given, and a 

 day will be set apart for the examination of the International 

 Electrical Exhibition, to be held at Philadelphia, under the 

 auspices of the Franklin Institute, and commencing September 2. 

 By an arrangement between the Canadian and United States 

 trunk lines, the members of the British Association will be 

 furnished with first-class passage from Montreal to Philadelphia 

 and return for 15 dollars (3/. is. 8</.), or for the single trip from 

 Montreal to Philadelphia for 9 dollars (1/. 17^.). It is to be 

 hoped that these rates will be further reduced before the members 

 of the British Association will be ready to take advantage of 

 them. 



The Executive Council of the International Health Exhibi- 

 tion have determined to hold an International Conference on 

 Education in connection with the Education Division of the 

 Exhibition : they have appointed a Committee of Management, 

 who have drawn up a programme. For convenience of discus- 

 sion all papers to be read will be printed beforehand, and they 

 will subsequently be published by the Executive Council. 

 Persons desirous of attending the Conference are invited to send 

 in their names to Mr. R. Cowper, Secretary to the Committee 

 of Management, International Health Exhibition, South Ken- 

 sington, to whom any inquiries can be addressed. The follow- 

 ing are the subjects for discussion : — I. Conditions of Healthy 

 Education. 2. Infant Training and Teaching : (a) Kindergarten ; 

 (/;) Instruction generally. 3. Technical Teaching : (n) Science ; 

 (i) Art ; (?) Handicrafts ; (</) Agriculture ; (?) Domestic Eco- 

 nomy. 4. Teaching of Music in Schools. 5. Museums, 

 Libraries, and other Subsidiary Aids to Instruction in Connec- 

 tion with Schools. 6. Training of Teachers. Under this head 

 will be considered the right professional preparation for teachers 

 in (a) elementary, (/>) intermediate and higher, (?) special and 

 technical schools. 7. Inspection and Examination of Schools : 

 (a) by the State ; (b) by the Universities ; (?) by other public 

 bodies. 8. Organisation of Elementary Education. 9. Or- 

 ganisation of Intermediate and Higher Education. 10. Organisa- 

 tion of University Education. 11. Systems of Public Instruc- 

 tion in various Countries. 



The Albert Medal of the Society of Arts has been awarded by 

 the Council of the Society, with the approval of the Prince of 

 Wales (the President), to Capt. James Buchanan Eads, "the 

 American engineer, whose works have been of great service in 

 improving the water communications of North America, and 

 have thereby rendered valuable aid to the commerce of the 

 world." 



