Nov. 19, 1 88 5 J 



NATURE 



69 



the greater part of the motion, is large relatively to the frictional 

 resistance of the suspended mass. 



Between ordinary earthquakes and tremors, on the one hand, 

 capable of observation by the inertia method, and slow earth- 

 tiltings, on the other, capable of observation by the equilibrium 

 method, it is at lea^t possible that there may be many move- 

 ments, not reducible to either type. For example, if successive 

 upheaval and subsidence of small amphtude \\ ere to occur with 

 a very long horizontal wave-length, and with a period of (say) one 

 or two minutes or more, it would be practically impossible even to 

 detect its existence by either of the methods named, unless by 

 chance it were repeated several times with uniform period in the 

 presence of a very frictionless vibrator whose free period 

 happened to agree nearly with the period of the disturbance ; 

 even then, no measurement of its amount could be made. We 

 are in fact forced to classify earth-movements under the two 

 heads which have been named, not because there is any necessary 

 discontinuity between the two, but because they must be treated 

 by two entirely distinct modes of observation. 



For the measurement of palpable earthquakes by the inertia 

 method, the writer has devised many instruments which have 

 been successfully applied to the registration of Japanese earth- 

 quakes, and which are describetl in a memoir on earthquake 

 measurement, published in 18S3 by the University of Tokio. He 

 has not attempted in any case to give the astatically suspended 

 mass three degrees of freedom, and notliing would be gained by 

 doing so. An instrument with two degrees of freedom is now ex- 

 hibited to the Association. It consists of an ordinary pendulum 

 coupled with an inverted pendulum, in such a manner that tlie 

 two bobs move together in any horizontal direction. This com- 

 bination of a stable with an unstable mass can be adjusted to 

 give any desired degree of astaticism. In practice it is con- 

 venient to allow the joint mass to have a free period of from five 

 to ten seconds, the period of ordinary earthquake waves being 

 much less than this. A long and light lever, pivoted to the 

 frame of the instrument at one point, and to the steady mass at 

 another, forms a registering index, by which a magnified trace 

 of the earth's horizontal movement is deposited on a fixed plate 

 of smoked glass with the least possible friction. 



In another instrument two components of horizontal motion 

 are separately determined, each by a horizontal pendulum, 

 tilted slightly forwards to give a small degree of stability, and 

 furnished with a multiplying pointer. In this instrument the 

 pointers trace the successive movements of the earth on a plate 

 of smoked glass which is kept revolving uniformly by clockwork. 

 The velocity and acceleration of the movements are deducible 

 from the records. This is the standai'd form of seismograph 

 employed by the writer, and, to make the information it gives 

 complete, another instrument for registering (on the same plate) 

 the vertical motion of the ground is added. 



The vertical-motion seismograph is a horizontal lever, sup- 

 ported on a horizontal fixed axis, and carrying at one end a 

 heavy mass. A spring attached to a tixed point above holds up 

 the lever by pulling on a point near the fulcrum. To make the 

 mass nearly astatic tlie point at which the spring's pull is applied 

 is situated below the horizontal line of the lever, so that when 

 the spring, by (say) being lengthened, pulls with more force, the 

 point of application moves nearer the fulcrum, and the moment 

 of the pull remains very nearly equal to the moment of the 

 weight. 



Apart from its application to palpable earthquakes the inertia 

 method is to be appUed to minute earth-tremors of the kind ob- 

 served in Italy by Berlelli and Kossi, which are probably to be 

 found wherever, and whenever, one searches for them with 

 sufficient care. Bui in dealing with them no mechanical means 

 of recording can well be applied, on account of its friction, and 

 a still more frictionless method of suspending the lieavy mass is de- 

 sirable. The writer prefers for this purpo-e a mode of suspension 

 based on Tchebicheif 's approximate straight-line motion ; and to 

 detect the movement of the ground he observes, by a microscope 

 fixed rigidly to the frame of the machine, the displacement of 

 the frame with respect to the suspended mass. This is Bertelli's 

 method, except for the substitution of a nearly astatic mass for 

 the stable mass used by him — namely, the bob of a short 

 pendulum — which of course gives a mi-leading magnification of 

 certain vibrations. 



The writer was recently requested by the Directors of the 

 Ben Nevis Observatory to design seismometers for use there, and 

 obtained a Government grant for their construction. The 

 equipment at Ben Nevis will include recording-seismographs. 



and a micro-seismometer of the kind just described. To measure 

 slow earth-tiltings an instrument is being constructed in which a 

 modification (due to Wolf) of d'Abbadie's arrangement (de- 

 scribed in Prof. Darwin's Reports) is followed. Light from a 

 lamp travels some twenty feet horizontally to a mirror inclined 

 at 45° to the horizon. It passes vertically down through a lens 

 which brings the rays into parallelism. They then strike two reflect- 

 ing surfaces — one the surface of a basin of mercury, the other a 

 plane mirror very rigidly fixed to the rock. The rays come 

 back to form two images near the source, and any relative dis- 

 placement of the two images is measured by a micrometer- 

 microscope. In the choice and design of this instrument the 

 writer has to acknowledge much assistance from Prof. G. H. 

 Darwin. This apparatus, like the others, was intended for Ben 

 Nevis, but a visit to the Observatory there has convinced the 

 writer that to use it on that site, and in the atmosphere which 

 prevails on the top, would be a matter of extreme difficulty, and 

 that, in the first instance at least, observations should be made 

 with it on lower ground. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE 



Cambridge. — Prof. P. G. Tait has been elected an 

 Honorary Fellow of Peterhouse ; and Mr. T. T. JefFery, M.A., 

 a Fellow of the same College. 



Mr. J. Larmor, M.A., of St. John's College, has been 

 appointed one of the University Lecturers in Mathematics, and 

 also Examiner for the First Part of the Mathematical Tripos of 

 1886. 



The Syndicate appointed to re-arrange the additional subjects 

 of the Previous Examination have reported in favour of adding 

 Elementary Dynamics to Statics, and reducing the Trigonometry 

 to what is needed for the Examination in Mecli.anics ; Mathe- 

 matical Honour students, they recommend, shall no longer be 

 required to pass this Examination, but instead be required to 

 pass in either French or German. Physical Science and Bio- 

 logy are still to receive no recognition even as optional subjects. 



Dr. Burghardt, Lecturer in Mineralogy in Owens College, 

 Manchester, is appointed to examine in Mineralogy in the 

 Natural Sciences Tripos ; Prof Ray Lankester, F.R.S., to 

 examine in Zoology and Comparative Anatomy in the same 

 Tripos, the First M.B., and the Special Examinations. 



Christ's College offers Scholarships and Exhibitions for 

 Natui"al Science, the Examination beginning January 5, 1886. 

 The Examinations at Jesus College begin on the same day. 



The Special Boards for Physics and Chemistry and for 

 Biology and Geology have issued the following notice with 

 regard to the First Part of the Natural Sciences Tripos : — 



In Part I. of the Examination all the questions will be of a 

 comparatively elementary character, and will be such as to test 

 a knowledge of principles rather than of details. Specimens 

 may be exhibited for description and determination. 



In Physics the questions will be limited to the elementary and 

 fundamental parts of th-i subject, and, in particular, special at- 

 tention will be paid to the definition of physical quantities, the 

 general principles of measurement, the configuration and motion 

 of a material system, the laws of motion, the comparison of 

 forces and of masses, and the properties of bodies. In Sound, 

 Light, Heat, Electricity and Magnetism, only the fundamental 

 laws, their simpler applications, and the experiments which 

 illustrate them, will be required. 



In Chemistry the questions will relate to the leading principles 

 and experimental laws of Chemistry, the properties of the com- 

 moner elements and their principal compounds, the outlines of 

 Metallurgy, and simple qualitative and quantitative analysis. 



In Mineralogy the questions will be confined to elementary 

 Crystallography, the general properties of minerals and th.- 

 special characters of those species only which are of comm >n 

 occurrence or of well-known mineralogical importance. 



In Geology the questions will be limited to Physical Geo- 

 graphy, the interpretation of the structure of the crust of the 

 earth and the history of its formation, so far as to involve only 

 the elementary parts of Palfeontology and Petrography. 



In Bot;my the questions will relate to the elementary parts of 

 Vegetable Morphology, Histology, and Physiology ; and to the 

 principles of a natural system of classification as illustrated by 

 the more important British natural orders. Candidates will be 

 required to describe plants in technical language. Questions 



