198 



KNOWLEDGE. 



May. 1911. 



the waves produced in the lake, which reached a height of ten 

 feet. Here and farther inland, some injury was caused by 

 earthquakes, more by the continual shaking than by the actual 

 strength of any shock, for none of them attained a destructive 

 degree of intensity. At the observatorv of Manila, nearly one 

 thousand shocks were recorded between the evening of 

 January 27th and February 7th, none of which in that city 

 reached an intensity greater than the fourth degree of the 

 Rossi- Forel scale of intensity. In other words, the strongest 

 were capable of m.iking doors, windows, fireirons, etc., rattle ; 

 they produced a trembling sensation like that felt on a station 

 platform when an express train passes. Other shocks, of the 

 third degree, were just sufficiently strong to be felt by human 

 beings. The great majority of the shocks were of the second 

 and first degrees of intensity ; they were microseismic move- 

 ments requiring rather delicate instruments for their detection. 

 The following table, founded on that given in Father Saderra 

 Maso's report, shows the number of shocks of each degree 

 registered at Manila from 11.6 p.m. on January 27th to 

 Februarv 7th. 



It will be noticed that the shocks were most frequent on the 

 day following the beginning of the eruption and on that after 

 the great explosion. .\s this occurred at 2.20 a.m. on January 

 30th, it is evident that the explosion caused a temporary relief 

 of the internal strains, such as might well gi\'e rise to the old 

 view according to which volcanic eruptions were the safety- 

 valves that shielded us from earthtjuakes, 



ZOOLOGY. 



By Proi-essor J. .Arthur Thomson, M..A.. 



BIRD - M.ARKIXC,. — The .Aberdeen University Bird- 

 Migration Inquiry, of which Mr, A. Landsborough Thomson 

 is the Secretary, aims at collecting more definite information 

 on the subject of the Migration of Birds by means of the 

 method of placing rings on the feet of a large number of 

 birds in the hope of hearing of the subsecjuent nunements of 

 some proportion of them. To this end the rmgs .u'c inscribed 



with the address " .Aberdeen University," and a number lor 

 number and letter combination) different in each case. The 

 rings are placed on young birds found in the nest, or on any 

 old ones that can be captured without injury. The rings are 

 of aluminium and extremely light, and do not inconvenience 

 the birds in any way. The marking work is chiefly carried on 

 in Scotland, notably in .Aberdeenshire, but is not confined 

 thereto. The Inquiry has the support of Mr. J. A. Harvie- 

 Brown. Mr. W'm. Eagle Clarke. Mr. W'm. Evans, and other 

 well-known Scottish ornithologists, and similar In<iuiries exist 

 in England and abroad. 



The coi)peration of all who take any interest in Natural 

 History questions is earnestly solicited in order to secure the 

 best results : — 



1. It is particul.irK- requested that all «ho nia>- hhoot. 

 capture, or kill, or e\en hear of any of our marked birds should 

 let us know of the occurrence. .As accurate particulars of 

 date and locality as possible are desired, but, above all, the 

 number (or number and letters) on the ring. Indeed, except 

 where it has been possible to reliberate the bird uninjured, the 

 ring itself should always be sent ; or the ring and foot, or even 

 the whole bird. We always refund postage if asked to do so. 



2. Cooperation is invited in the actual work of marking, 

 of any who are specially interested, and have some knowledge 

 of birds, and also time and opportunity for the work. The 

 necessary rings, schedules, and postage stamps, are supplied 

 by us without charge, and we undertake to let the marker 

 know of each case of a bird marked by him being recovered, 

 and to let him have copies of printed reports so far as 

 possible. 



The following results obtained at an early stage of the 

 work will ser\e to indicate what is to be expected from it ; 

 these are merely a few records which happen to be of con- 

 siderable individual interest : — 



A Widgeon duckling [Marcca pen dope), one of fi\i;' marked 

 in June, 1909, on Loch Brora, Sutherland, Scotland, 

 was taken in a duck-decoy in Province Groniugen, 

 north-eastern Holland, on 3rd September. 1909. This 

 bird was thus only three months old when it was found 

 more than 500 miles from its birth-place. .A second 

 member of the brood was shot on the Trent, near 

 Retford. Lincolnshire. England, in January, 1911, 

 lia\ing wiirn the ring for a year and a half, 



.An adult Swallow \Hinindu nistica) caught and marked 

 at a farm near Tunbridge Wells, Kent, England, in 

 June, 1909. was re-caught at the same farm in 

 June, 1910. 



Five Lapwings iVanelliis vulgaris) marked as chicks in 

 the North-east of Scotland, in the summer of 1910, 

 were shot respectively in Counties Tipperary, 

 Roscommon, Cork, and Limerick, Ireland, and in 

 Southern Portugal, during the winter 1910-11, 



,A Song-Thrush iTiirdiis nii(siciis), one of a brood marked 

 as chicks in the nest at Skene, .Aberdeenshire, in early 

 June, 1910, was shot near Leiria, Portugal, in early 

 November of the same year. The localities are about 

 one thousand two hundred and fifty miles apart. 



DISCS FOR SOL.XR PR( )J I':CTION, 

 By JOHN McH.VRG, M,A. 



In the series of maps for solar projection of which an example 

 is printed on the following page, the graduation to intervals of 

 10 in latitude and longitude is only carried to the fortieth 

 parallel of latitude. For convenience in estimating the 

 diameters of sunspots, a portion of tlTE central meridian is 

 divided into degrees, one of .which is equal to seven thousand 

 five hundred and fifty-four miles. The heliographical latitude 

 of the centre and the position-angle of the solar axis are 

 considered positive, the former when the North Pole is tilted 

 toward the observer, and the latter when it is inclined from 

 the north point toward the east ; this happens on the dates 

 when the directing lines at the right-hand side of the map are 

 above the equator. It will be observed that with the exception 

 gf a brief period about the time of the solstices, the above 



quantities have the same sign throughout the rest of the year. 

 The solar image, when projected on the disc by a refractor 

 provided with an astronomical eyepiece, suffers reversal from 

 left to right, after the fashion of images in a plane mirror or 

 that of the sun in a diagonal. The correct position-angle of 

 the disc may be easily obtained by stretching a hair tightly 

 across the field of the eyepiece a little beyond its focal plane. 

 This is then turned till the image of a spot runs along the hair, 

 or in its absence by depressing the image till a mere thread of 

 light remains above the crossvvire. The coincidence of 

 ecfuators of image and disc is then secured by causing the 

 appropriate directing line on the disc for the date to coincide 

 with the image of the crosswirc, intermediate positions to those 

 gi\en being supplied by estimation or measurement. 



