May 4, 191 6] 



NATURE 



201 



Bridge Company, and is now a professor in Sibley 

 College, Cornell University, His experience, 

 therefore, leads us to expect that his volume will 

 contain much matter of service to structural 

 draughtsmen, and that the treatment will be suit- 

 able for students. The early demand for a 

 second edition is evidence that the author has 

 been successful in his treatment, and this is con- 

 firmed by inspection of the text. The book does not 

 pretend to deal with the mechanics of materials 

 — the student is referred to other books for this 

 — and the reader who has studied materials will 

 find his knowledge drawn upon throughout the 

 book in application to a large number of struc- 

 tures. Sufficient is given at ev6ry step to enable 

 the student to understand which particular theory 

 is being applied. There are practical examples, 

 fully worked out, of every class of structure dis- 

 cussed, and the formulae used in practice are 

 explained clearly. A large number of exercises 

 to be worked by students is included. 



Although the methods of design are American, 

 the British student and designer of structures will 

 profit considerably by going through this volume. 

 We have read chapters xvii. and xviii. with par- 

 ticular interest ; these deal respectively with 

 retaining walls and with bins for holding grain 

 and coal ; the latter chapter is exceptionally com- 

 plete, and, as is usual throughout the book, con- 

 tains typical examples worked out. 



Rambles in the Vaudese Alps. By F. S. Salis- 

 ; bury. Pp. X+154. (London: J. M. Dent and 



Sons, Ltd., 1916.) Price 2S. 6d. net. 



Mr. Salisbury's book gives a pleasant account 



of a summer holiday in 1908, spent at Gryon in 



anambitious excursions among the limestone Alps 



Df the western Oberland. The fine views of such 



Tiountains as the Diablerets and the Grand 



jMuveran, in the immediate neighbourhood, and 



i:he magnificent gable-end of the Dent du Midi on 



ihe other side of the Rhone, as they rise above 



(•lopes of green pasture and dark pine-wood, 



jHake this an unusually attractive district. 



I The author writes, not for geologists or botan- 



|5ts, but for lovers of mountain scenery and 



jiountain flowers. As, however, he did not reach 



'ryon until the beginning of August, he was too 



ite for the blossoms which, some five or six 



•eeks earlier, make the meadows, from three to 



[Ve thousand feet above sea-level, a carpet of 



jiany colours. These, in that month, have given 



ace to less graceful kinds, such as the yellow 



|id purple gentian, the white hellebore {Veratrum 



niim), and the monkshood. But his visits to 



summits and passes, some three thousand 



above the level of Gryon, were rewarded by 



1 lovers of the mountain air as the Dryas 



,-'petala and the alpine aster, the little blue gen- 



I'-ns, and even the edelweiss. Some photographs 



" the flowers, by Mr. Somerville Hastings, add 



the interest ot the book, and it is one which 



tourist who loves to linger rather than to 



"v, and desires to learn a little about the 



Hnt world of the Alps, will find a useful and 



ajractive companion. 



NO. 2427, VOL. 97] 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for 

 opinions expressed by his correspondents. Neither 

 can he undertake to return, or to correspond with 

 the writers of, rejected manuscripts intended for 

 this or any other part of Nature. No notice is 

 taken of anonymous communications.] 



Zeppelin Notes. 



As one who happened to be in a region which came 

 in for attention from Zeppelin bombs, I have jotted 

 down some of the points of more immediate interest 

 which stand out from an experience in which every- 

 thing was rather blurred : — 



The bombs could be heard approaching as they 

 rushed through the air. The whistling noise — a little 

 like the tearing of calico or the noise made by a 

 gigantic rocket — became a crescendo shriek of terrific 

 intensity just before the bomb struck the ground and 

 the explosion occurred. In the present instance I 

 estimated the height of the Zeppelin as about 4000 ft., 

 and, neglecting air resistance, this would give the 

 bombs a final velocity of about 500 ft. per second. 

 The actual speed was probably less than this, and is 

 considerably less than the velocity of sound (iioo ft. 

 per sec), which accounts for the fact that the bombs 

 can be heard before their arrival. 



Standing as I was at about 200 yards from where 

 one of the bombs fell, the noise of the actual explosion 

 did not appear to be very loud. The reason is prob- 

 ably to be sought in the almost complete numbing of 

 one's senses. All one could do was to stand stock- 

 still and wait for the next bomb. The feeling was 

 much the same as if one had been given a hard blow 

 between the eyes with a bolster or some relatively soft 

 object. I heard a piece of bomb "zip" past me, and 

 afterwards found it embedded in a balk of timber 

 about two yards from where I was standing. A huge 

 cloud of black smoke arose into the air, reminding 

 one of the photographs of Jack Johnson shells burst- 

 ing. 



The results of an explosive bomb show curious freak- 

 ishness, especially in enclosed spaces. Evidently 

 " pockets " of high pressure result in various direc- 

 tions, and the destruction is confined to the direction 

 of these pockets. Considerable damage may be caused 

 apparently by the air rushing in to restore the pressure 

 after a high-pressure wave has passed forward. For 

 example, one bomb fell near a small outhouse. The 

 doors were blown bodily inwards — mostly owing to 

 the hinges and frames breaking loose — vet the sur- 

 rounding wall of the house was "started" outwards. 

 One pane of glass in a window-frame disappeared, 

 while an adjacent pane similarly situated was un- 

 damaged. The lid of a kettle was deftly blown off by 

 the air wave going down the spout, the kettle being 

 undamaged. 



The bombs fell in soft marshy ground, and the 

 effects of the explosion were very local. Apart from 

 flying missiles, the danger zone did not appear to 

 exceed 25 yards or so. Windows, about 15 vards 

 away, on the side of an outhouse remote from the 

 explosion were quite intact. 



Pieces of one of the explosive bombs perforated 

 some steel plates standing vertically about 10 yards 

 away. The edges of the holes were rounded, and 

 showed undoubted signs of fusion, due no doubt to the 

 speed of the shearing. In one instance a piece of the 

 phosphor-bronze casing of the bomb penetrated a steel 

 plate more than i in. thick. 



The holes caused in the soft clayey ground by the 

 explosive bombs were approximately conical, some 

 10 ft. across, and about 4 ft. deep. 



The incendiar}- bombs could be heard coming with 



