514 



NATURE 



\_Scpt, 29, )88i 



upon the same slope have divided the masses of the rocks 

 into large pieces, whilst the frequent earthquakes of the 

 last months have given rise to large crevices in the slates 

 and limestones. Already on September 9 it was perceived 

 that the soil at the quarry was in slow motion, and a 

 house situated immediately below was evacuated. Two 

 days later, between five and six o'clock in the afternoon, 

 it was seen that the forest on the slope of the mountain 

 began to mo\e, the trees being bent like a field of corn 

 duringa strongwind; they then rushed down.togetherwith 

 the rocks situated above the quarry, breaking up into t'^ou- 

 sands of pieces. This formidable stone avalanche reached 

 the village, the trees were bent like straw, and the houses 

 moved by the pressure of air pushed by the landslip. 

 Men and house; were thrown on the opposite side of the 

 valley, smashed against rocks, and buried by the landslip, 

 which, as in the catastrophe of the Rossberg, crossed the 

 valley and rose up-hill on its opposite side. The first 

 landslip destroyed that part of the Elm Commune which 

 is named Unterthal ; but a second one followed imme- 

 diately, destroying the village, and throwing the houses 

 on the opposite side of the valley, one kilometre wide. 

 The picturesque valley of Unterthal is now covered with 

 a mass of mud, earth, and stones, thirty to forty metres 

 thick, on the surface of which are seen blocks of the size 

 of a house. The length of the landslip is about two kilo- 

 metres, and the opposite side of the valley is covered 

 with stones and blocks on a space of about 100 metres. 

 The Sernft River, which flows in the valley, is barred by 

 the ch'bris, and has formed a small lale. The number 

 of persons killed is about 160. Another small landslip 

 occurred on the following day, and ihe slope of the moun- 

 tain continues to be in motion. .According to a report of 

 Prof. Heim the remnant of the village is also threatened 

 by a landslip, the Risikopf, or Gros^kopf, being creviced 

 and undergoing subsidences which render a landslip 

 most probable, not so large, however, as the preceding 

 one. 



The Times Geneva correspondent writes under date 

 September ig : — "According to the measurements and 

 estimates of Prof. Heim, of Zurich University, who has 

 just visited Elm, the eanhslip of yesterday week, though 

 less de-tructive of human life than the earthslip of Plurs 

 and Goldau, probably exceeds m extent eiiher of those 

 catastrophes, great as they were. The portion of the 

 Tschingel Alp which broke away from the parent moun- 

 tain measured at its base 400 metres by 350 metres. The 

 length of its projection outwards cannot, of course, now 

 be asccrtainecl. The length of what Prof. Heim calls the 

 debris iUft'Am is 1500 metres, and varies in breadth from 

 jOo to 400 metres. The distance of the extreme end of 

 the stream from the place " hence it broke away is 2000 

 metres. The extent of the vailey bottom, which is toler- 

 ably even, covered by debris is computed at 570,000 

 metres, while the entire mass makes a total of 900,000 

 square metres. From the lower part of the valley to the 

 upper joint of rupture the height is 620 metres. The fall 

 was, therefore, a little over 2000 feet. The lowest esti- 

 mate of the contents of the slip, according to the ad- 

 measurements of the engineers, is 10^000,000 cubic metres. 

 It contains, says the Professor, enough stone to build two 

 cities as large as Zurich, and the population of Zurich is 

 76,000. Some of the blocks, which are heaped 112 

 metres higher than the village of Elm, measure 1260 

 cubic metres, and are estimated to vTeigh 3300 tons. If 

 the other earthslip, which is regarded as imminent, 

 should take place, all that remains of Elm will be 

 destroyed." 



The heavy rains of the last weeks have caused several 

 other landslips in Switzerland and Savoy. In the Upper 

 Singine, in the canton of Freiburg, the soil is in slow 

 motion in the valleys of the Gcrine and Singine rivers, 

 and a landslip of some importance has occurred at 

 Planfayon. Another landslip occurred on September 2, 



close by Bernex village, on the slope of the Dent d'Cch, 

 and it is rather remarkable by the circumstance that it 

 occurred in a broad open valley where one never would 

 suppose the possibility of a gliding of rocks. 



A further interesting result of the recent heavy rains is 

 that the Lake of Bicune, which is soinewhat lower than 

 that of Neuchatel, is now so full that its water runs into 

 the Lake of Neuchatel, inundating its shores. 



PHENOMENA DEVELOPED BY HELIOSTATIC 

 STAR-DISKS 

 A HELICSTAT of the highest class is doubtless 

 -'*- beyond the means of ordinary observers, but such 

 an instrument as the one now described is readily obtain- 

 able. Three sets of achromatic lenses forming a focal 

 power of forty at ten inches, or a miniaturing power of 

 one-fortieth, are in general sufficient. If formed into a 

 microscopic object-glass, the front is turned towards the 

 sun. The glass then refracts a beautifully small star-disk, 

 which, owing to the large angular aperture of the cont- 

 bination, remains steadily in view for several hours. The 

 optical characters of this di^k vary considerably with the 

 quality of the lenses ; practically a very fine one-quarter 

 by Powell and Lealand produces disks of remarkable 

 beauty and precision. In some cases a plane mirror is 

 conveniently attached to reflect the oblique solar rays. 



The instrument thus provides a stationary solar star- 

 disk for continuous observation. No clockwork or ma- 

 chinery is required. The size of the disk is one-fourth of 

 the sine of the solar diameter, or nearly 45-ro,oooths of 

 an inch. 



A more brilliant form of surpassing effulgence is occa- 

 sionally employed by a 3-inch lens placed before a right- 

 angled prism -An aerial image of the sun thus produced 

 outshines the electric light. These disks are viewed at a 

 distance of ten feet. 



It is proposed to describe first their use in microscopic 

 research, and secondly for telescopic vision. 



I. Microscopic Rese.arch 

 The Miiialure Method.— X strong plate fitting the 

 upper stage of the microscope by means of screws is 

 pierced in the centre by an aperture carrying the 

 "societies" standard screw, into which an objective can 

 be firmly screwed. The stage motions then give readily 

 the necessary adjustments for coincidence of optical 

 axes. This is called the stage-holder. All previous 

 methods of fixing the objective in the sub-stage have 

 been abandoned ; the necessary steadiness being almost 

 unattainable. 



Phenomena of Heliostatie Star-Disks produced by the 

 One quarter. — Stage-holder armed with an inverted l-32nd 

 water-immersion. The miniature of the star-disk is now- 

 viewed microscopically with a i-i6th immersion. When 

 both of these objectives are adjusted for the most bril- 

 liant vision, distant foliage is distinctly visible. A flag- 

 staff carrying the Union Jack iSo yards away displays its 

 double cross. The fine lightning-rod surmounting it is 

 distinctly visible. Houses on a hill glisten in the sun- 

 shine ; but conspicuous above all is the minute solar star- 

 disk blazing with all the glory of a midday Sirius at the 

 open window-sill. 



Here the favourite tests for telescopic preci-ion come 

 richly into play. A minute brilliant bead surrounded by 

 the most intensely black ring — the more wonderful as the 

 brilliance seems to heighten its rare and beautiful deli- 

 cacy and blackness — comes up and plays into expanding 

 coloured rings on each s'de of the principal focal poiiit. 

 (The delicate beauties of this exquisite phenomenon can- 

 not well be seen without an exceedingly delicate fine focal 

 adjustm.ent.) The focussing wheel (constructed for the 

 lightest contact) is divided into 132 parts ; twenty-six give 

 a focal plane the loooth of an inch deeper or higher, 



