January 13, 189S] 



NATURE 



249 



investigation, and to Dr. F. Omori, our knowledge of 

 annual, semi-annual, diurnal, and other earthquake 

 periodicities has been placed on a more certain basis 

 than it formerly occupied. 



Without entering into the observations which have 

 been made upon magnetic phenomena, sea waves, sound 

 phenomena, the behaviour of lower animals, and a variety 

 of other subjects connected in a greater or lesser degree 

 with exhibitions of seismic force, what has been said 

 indicates that the study of earth movements, which we 

 feel, have not been without profit. 



In Japan, at its University, there is a chair of Seis- 

 mology ; a bureau, which in 1895 controlled 968 observing 

 stations ; whilst the Government give liberal support to a 

 committee of engineers and architects, whose duty it is 

 to carry out investigations which may lead to the mitiga- 

 tion of earthquake effects. 



Notwithstanding the opportunities which Japan offers 

 to make such investigations, it is worthy of note that two 

 trained men were ordered by the Government 

 of that country to report upon the recent earth- 

 quake in Assam. This they have done, and no 

 doubt Japan is now in a position to avoid forms 

 of construction of which she was hitherto without 

 experience. J. Milne. 



( To be cotittnued). 



THE AREQUIPA OBSERVATORY. 



pROF. PICKERING has conceived and car- 

 -^ ried to a successful issue many projects that 

 require both mechanical skill and confidence in 

 his resources. In the gradual development of 

 these schemes, we have seen the modest row of 

 volumes, that contained the annals of the Harvard 

 Observatory prior to his directorate, increase to 

 imposing proportions. We know how deftly he 

 holds the strings that control the operations of 

 many departments outside Harvard, and how 

 efficiently he copes with the work that a whole 

 army of astronomers submits to his examination. 

 But assuredly the equipment and maintenance of 

 the observatory at Arequipa will be remembered 

 as one of his most successful achievements. We 

 are apt to think of a subsidiary observatory, 

 especially when situated in a position difficult of 

 access, as one temporarily occupied for a definite 

 purpose, and requiring but few instruments, 

 mounted in buildings of slight construction. But 

 the energy of Prof. Pickering has established in 

 South America an observatory that a State 

 government, having the resources of a public ex- 

 chequer at its will, might look upon with satisfac- 

 tion. We reproduce in Fig. i (p. 250) the general 

 appearance of this astronomical station, some 8000 

 feet above the level of the sea, and a mere glance 

 will show or suggest how varied must be the work 

 of the observatory, in which all the telescopes 

 under the different sheds are kept constantly employed 

 through every clear night. In the illustration the observer's 

 residence is on the extreme right. Starting from that 

 point and taking the several buildings in order as we 

 approach the left, we have first of all a laboratory with 

 developing rooms attached, next a shed containing a 5- 

 inch visual telescope, which leads on to another containing 

 a 20-inch mirror of short focal length, figured by Dr. 

 Common for the observation of the solar eclipse of 1889. 

 We then pass a building containing the principal clocks 

 and a transit instrument, and come to that containing 

 the Bache telescope of eight inches aperture. Next to 

 this is the 13-inch Boyden telescope under a cylindrical 

 drum roof To the left of this, and before we come to 

 the buildings occupied by the assistants, is a telescope 

 with a Voigtlander portrait lens as an objective in which 

 are taken photographs of four hours' exposure of faint 



NO. 1472, VOL. 57] 



nebulous regions of considerable extent. To this list of 

 instruments must now be added the Bruce photographic 

 telescope, having an objective doublet of 24 inches 

 aperture, and from Prof. Pickering's last report we learn 

 that a transit photometer similar to that in use at Harvard 

 has been erected. Photographs of all the bright stars 

 from the North to the South Pole are now obtained when 

 they cross the meridian on every clear evening, either at 

 Cambridge or Arequipa or both. 



We shall get a good idea of the use to which these 

 instruments are put if we describe some of the illustrations 

 that Prof. Pickering has given in the volume containing 

 the " Miscellaneous Investigations of the Henry Draper 

 Memorial." We have first of all a picture of the Southern 

 Cross on which abuts a portion of Herschel's Coal-sack 

 region, taken with the Bache telescope, exposure 127 

 minutes, covering an area ten degrees square. We might 

 make this plate the excuse for discussing several points 

 of great interest. First, should photographs represent 



Fig. 6. — Map showing the origins of 8331 shocks recorded between 1885 and 1892 in 

 Japan. The large dots indicate the positions of active volcanoes. The small dots 

 indicate the origin of different earthquakes which group themselves into fifteen 

 districts, each marked by a large numeral. (Milne.) 



the stars on paper as positives or negatives ? Prof. 

 Pickering, by his practice, is clearly in favour of ex- 

 hibiting the stars as black dots on a white ground. In 

 this decision he has been guided by the use of ordinary 

 star charts, in which there has never been any question 

 as to the most convenient method of representing stars, 

 and to which astronomers have already accommodated 

 themselves. With regard to the important question of 

 the scale to be adopted, and which in this telescope gives 

 three minutes to the millimetre, it will be admitted that 

 it is too small for star charts, if faint stars are to be 

 represented. Prof Pickering says distinctly that the 

 images are too near together to be conveniently studied. 

 It is mainly for this reason that we do not reproduce the 

 plate, which would have been interesting since it affords 

 a good illustration of the difference between photographic 

 and visual magnitudes. 7 Crucis, which has a spectrum 



