September, igo6.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



537 



its form of a period when it was pear-shaped. Ihe 

 waist of the pear would be its weakest region or Une, 

 and along this line any strain resulting Irom sudden 

 disturbances of the earth's axis would be felt more 

 severely than anywhere else. If the regions along 

 this hne of weakness had a predisposition or 

 susceptibility to earthquake movement, then in a time 

 of stress we should expect earthquakes to be manifest 

 chiefly along this line. That, according to Professor 

 Milne, is wnat we found last year. A glance at the 

 map shows that of the 57 widespread earthquakes of 

 last year, the great majority were confined to a circle 

 passing from Central America through the Azores, the 

 Alpine, Balkan, and Himalayan ranges into the East 

 Indian Archipelago. The quiescence of districts which 

 do not lie on this band was very marked during 1905, 

 though it has now been sensationally interrupted by 

 the V'alparaiso earthquake. There was a destructive 

 earthquake in Calabria on September 8, 1905, but Pro- 

 fessor Milne is not sure whether it was in any way con- 

 nected with the relief of volcanic stress which began as 

 early as May, 1905, and culminated in the violent erup- 

 tions at Vesuvius in April, igo6. The largest earth- 

 quakes, eclipsing this, or the Indian one of April 4, 

 1905, or even that which on April 18 of this year 

 devastated Central California, were two which occurred 

 in Central Asia in July of last year. No accounts of 

 destruction, however, reached England, so that the dis- 

 tricts where they occurred must have been sparsely 

 populated. One of them was felt at Tomsk, in Siberia. 

 Other observations in Professor Milne's report dis- 

 closed the interesting suggestion that on the west side 

 of the Pacific earthquakes are more frequent in summer, 

 while on the eastern side they are more frequent in 

 winter. It is suggested that an explanation can be 

 found in the seasonal alternation in the flow of ocean 

 (Uirrents, the oscillation of sea level, and the changes 

 in barometric gradients — phenomena which are all con- 

 nected with one another. The most curious observa- 

 tions in the report are, however, as follows : — " It has 

 been found that under certain but frequently recurring 

 conditions the two opposite sides of a valley move in 

 opposite directions at the same time. On bright, fine 

 days the inclinations of the sides of a valley decrease. 

 At night they increase. A valley may, therefore, be 

 supposed to open and close. These conclusions, which 

 do not necessarily apply to all valleys, are based on 

 observations taken in two very different localities. The 

 first were made in Tokyo, Japan, by means of horizontal 

 pendulums giving continuous photographic records, in- 

 slallcd on the two sides of a valley cut in alluvium. 

 The phenomena may be due to the general warping of a 

 district under the influence of solar radiation, or to 

 the differential effects of loading and unloading of por- 

 tions of the same. During the clay the sides of a valley 

 covered with vegetation lose load by evaporation and 

 transpiration, and, therefore, underground drainage, 

 tending to carry a water load to the bottom of a valley, 

 is reduced. At night, with the cessation of these pro- 

 cesses, the load at the bottom of a vallev is increased. 

 At that time streams and certain wells carry their 

 greatest quantity of water. It is, therefore, at night 

 that a valley may be expected to sag downwards, a 

 suggestion that finds support in the observation that 

 during wet weather, when we see streams in flood, the 

 sides of the bounding valley approach each other in a 

 marked manner. The conclusion is th;it as the world 

 turns before the sun its surface is measurably smoothed, 

 while at night the frerklings on its face arc measurably 

 increased." — E. .S. O. 



A Great Catalogue of 

 Double Stars. 



It is only within the last two or three centuries that it 

 has been recognised that there are such things ns 

 " Double .Stars " ; that there are systems where two or 

 more suns share the supreme control; unlike the case of 

 our own system wherein our sun, lord paramount in its 

 own family, exercises a single and undixided sway, 

 the first star to be noted as double was Zeta Ursae 

 Majoris, the " Star of the Girdle," discovered to be 

 double by the astronomer Riccioli about the middle of 

 the seventeenth century. It is a curious coincidence 

 that this same star had also the distinction ot being the 

 first to l)e photographed as double, and again its com- 

 ponents were the first to show themselves 10 be spectro- 

 scopic doubles. 



the first great worker on double stars was Sir 

 William Her.schel, a century and a half later than 

 Riccioli. He observed and catalogued them, not lor 

 his interest in them as such, but because he hoped to 

 employ them in finding the parallaxes of the fixed stars. 

 Beiore his day instruments were neither sufficiently 

 powerful nor sulhciently refined to render possible the 

 delicate measurements needed in such an inquiry. But 

 Herschel was himself a great instrument maker, and 

 was, therelore, himself aale to o\ercome much of the 

 instrumental dilliculty ot the problem; the outstanding 

 difficulties he proposed to avoid by contenting him.sell 

 with determining, not the absolute parallax of a star, 

 but its relative parallax as compared with one which 

 was at an indefinitely greater distance from us. His 

 plan, therefore, rested upon the assumption that where 

 we have two stars apparently close together in the sky, 

 the fainter star is really immensely more distant than 

 the brighter, and is only seen near it because the two 

 chance to bje nearly in the same line of sight. His plan 

 failed because the faint comparison stars, which he 

 chose, proved in so many cases not to be far distant 

 from the stars whose parallaxes he sought, but to be 

 so close that they were strongly bound together by 

 gravity and moved together through the universe. The 

 result of his inquiry, however, was that he produced 

 the first catalogue of double stars. Herschel's eminent 

 successor in this class of observation was the 

 Russian astronomer, W'ilhelm Struve. He began his 

 astronomical career in 1813, and in 1837 he published 

 at .St. Petersburg his great work, generally known as 

 the " .Mensurie ^licrometrica?," containing the positions 

 ot 2,(140 double stars. 



.\bout a quarter of a century ago Mr. Thomas Lewis, 

 the -Superintendent of the 'lime Department of the 

 Royal Observatory, Greenwich, began in his leisure 

 time a study of this great catalogue of Struve 's, 

 collating all the measures of the objects contained in it 

 which he could gather from every available source. 

 The result of this study showed that many of Struve's 

 pairs had been neglected by observers, and about twelve 

 years ago, at ^lr. Lewis's request, the Astronomtr- 

 Royal granted him facilities for having these objects 

 measured by the great Grubb refractor of j8 inches 

 aperture, belonging to the Royal Observatory, Green- 

 wich. This enabled Mr. Lewis to complete his study 



