190 



NATURE 



TApril 24, 191, 



except by sliding one sheet over the other, when the 

 motion of some of the dots with respect to the others 

 immediately betrays its situation. R. S. Capon. 



Oxford. ' 



Mr. M. E. J. Gheury concludes a note in the issue 

 of Nature of March 27, relating to the gain of defini- 

 ;;>>n obtained by moving a telescope, with the words : 

 " Perhaps some of your readers have noticed some- 

 thing similar and could throw a little light on this 

 mysterious phenomenon." 



By a curious coincidence "something similar" did 

 come to my notice just one day previous to my read- 

 ing of Mr. Gheury's note. I do not propose to throw- 

 any light on the question, nor do I wish to imply 

 that there is anything more than an accidental and 

 external similarity between the two cases in question. 

 Rut it may not be out of place to direct attention to 

 a peculiar observation recorded in The Mechanic's 

 Magazine of the year 1829, and rescued from oblivion 

 in a recent number of the German periodical Pro- 

 methcus. The experiment is extremelv simple, and 

 can be repeated by anyone with the very simplest 

 materials. 



Take a piece of paper of such thickness that when 

 it is laid over a sheet of printed matter the characters 

 just show through but cannot be read. Place this 

 over a page of printed characters, move it about with 

 a circular motion, and you will no doubt be surprised 

 to find that now the print shows through and can 

 be read with comparative ease. It is, of course, 

 necessary to adjust the thickness of the paper and the 

 size of the type, but two or three trials are sufficient 

 to determine the right conditions for the experiment. 

 Alfred J. Lotka. 



New York, April n. 



THE NEW SEISMOLOGY. 



FOR very many years past in Italy, and to a 

 lesser extent in other countries, earthquakes 

 had been recorded, while a few private individuals 

 collected and analysed earthquake statistics. 

 These, however, were the days of seismoscopes 

 and the old seismology. The new seismology did 

 not come until macroseisms had been measured 

 and teleseisms had been discovered. With their 

 arrival new lines of physical, and particularly geo- 

 physical, research were opened for exploitation. 

 Commencing in Japan, the desire to record and 

 discuss the felt and unfelt palpitations of our 

 earth spread like an epidemic round the world. 

 In 1S80 the Seismological Society of that country 

 was founded, and the twenty volumes which it 

 issued contain initiatives for very many of the 

 investigations carried out since that date. When 

 this society ceased to exist the Japanese Govern- 

 ment established an Earthquake Investigation 

 Committee, which up to date has published more 

 than eighty quarto volumes. 



In the early days attention was first directed 

 towards obtaining instruments which would give 

 actual measurements of earthquake motion. 

 Steady-point instruments were devised, and, for 

 earthquakes we feel, are now in use throughout the 

 world. From a knowledge of the actual nature 

 of earthquake motion derived from these instru- 

 ments, new rules and formulae for the use of 

 engineers and builders were established. To test 

 NO. 2269, VOL. 91] 



the suggested new departures in building and 

 engineering practice, structures in brick and other 

 materials were fixed upon platforms actuated by 

 powerful machinery and subjected to movements 

 closely corresponding to those of heavy earth- 

 quakes. The results of these investigations in 

 Japan and other countries have been extensively 

 applied in the construction of piers for bridges, 

 tall chimneys, walls, ordinary dwellings, embank- 

 ments, reservoirs, &c. Inasmuch as the new types 

 of structure have for very many years withstood 

 violent shakings, while ordinary types in their 

 neighbourhood have failed, it may be inferred that 

 much has already been accomplished to minimise 

 the loss of life and property. 



The application of seismology to the working 

 of railways, particularly in Japan, led to the 

 localisation of faults on lines, and alterations in 

 the balancing of locomotives. The result of the ' 

 latter has been to decrease the consumption of 

 fuel. 



Later, instruments were devised to record earth- 

 quake motion which cannot be felt, with the result 

 that a person living in any one part of the world 

 can record and obtain definite information about 

 any large earthquake originating even so far off 

 as his antipodes. These records of the unfelt 

 movements of earthquakes have from time to time 

 indicated the position, the time of occurrence, and, 

 what is of more importance, also the cause of cer- 

 tain cable interruptions. The practical importance 

 of this latter information, especially to communities 

 which may by cable failures be suddenly isolated 

 from the rest of the world, is evident. 



The many occasions on which earthquake 

 records have furnished definite information respect- 

 ing disasters which have taken place in distant 

 countries, corrected and extended telegraphic re- 

 ports relating to the same, is another illustration 

 of the practical utility of seismic observations. 

 Seismograms have frequently apprised us of sea 

 waves and violent earthquakes in districts from 

 which it is impossible to receive telegrams, while 

 the absence of such records has frequently indi- 

 cated that information in newspapers has been 

 without foundation or at least exaggerated. 

 Localisation of the origin of- these world-shaking 

 earthquakes, besides indicating sub-oceanic sites 

 of geological activity, indicates positions where the 

 hydrographer may expect to find unusual depths. 

 They have also shown routes to be avoided by 

 those who lay cables. 



Seismograms of unfelt movements throw light 

 upon what have but recently been regarded as 

 unaccountable deflections in the photograms from 

 magnetographs, barographs and other instru- 

 ments sensible to slight displacements. They have 

 also explained unusual rates in certain time- 

 keepers. 



Among the very many scientific results which 

 the new seismologv has contributed to science is 

 that it has given us the velocities at which motion 

 is propagated in various directions through the 

 world. Until these observations had been made 

 our knowledge respecting the interior of the earth 



