60 



DISCOVERY 



It may be breathed apparently with impunity, but the 

 trouble comes later. 



Chloropicrin was one of the chief lachrymators or 

 weeping pases, and was used effectively, even at a 

 concentration of one part in a million, against troops 

 doing any work in which weeping rather interfered 

 witli things. Mustard gas was an irritant which even 

 in very small amounts had a very inflammatory effect 

 on the skin, the more insidious because it was not 

 immediate. It produced serious sores at the parts 

 affected, notably on the eyes, leading to many cases of 

 permanent blindness, and to an enormous number of 

 cases of temporary bUndness. 



These are the best known, but more irritating and 

 more deadly gases were being experimented with 

 towards the end of hostilities. It is rather curious 

 that prussic acid, which is associated in most minds 

 with sudden death, was used so little. The reason for 

 this is that, except in large concentration, its effect 

 is very mild. Also it is a very simple gas to secure 

 protection from with a respirator. 



The first respirator issued to our troops after the 

 original mouth-pad had been superseded, consisted of 

 a flannel helmet with mica eyepieces, which was puUed 

 over the head and tucked in under the collar. 

 Impregnated in the flannel was a solution of " hypo " 

 and other materials for absorbing the chlorine. Later 

 patterns of this type were provided with glass windows 

 for the eyes, and a rubber valve for exhaling the 

 breathed air. After a time a box respirator was 

 introduced, and this completely superseded the helmet 

 t3:pe. This respirator consisted of a small box fiDed 

 with granules of specially prepared charcoal, which 

 was guaranteed to absorb nearly every kind of poison 

 gas known. It was connected with the piece that 

 covered the face by a flexible rubber tube. A chp 

 gripped the nose in a most convincing manner. The 

 breathing in and out was done through the mouth 

 by means of suitable valves. 



It was a simple device, comfortable enough, and 

 ever\'one who was in France had the pleasure of 

 drilling in it. It gave complete protection against 

 most of the poison gases used, and when the charcoal 

 deteriorated it could be easily replaced. 



It is the opinion of a speaker at the last meeting of 

 the British Association that poison-gas warfare is not 

 so inhuman as it is commonly supposed to be. The 

 argument was, that granted that human beings must 

 die or suffer so that military objects may be gained, 

 then such objects may be attained by the use of poison 

 gas with less loss of life and permanent injurj' than by 

 the employment of high explosives. 



We agree, but we hope that this type of warfare is 

 ended for ever. 



A. S. Russell. 



Correspondence 



METEORIC SHOWERS AND COMETS 



To the Editor of Discovery 



Sir, 



Tliough the practical identity of certain meteoric 

 systems with comets has been an acknowledged fact for 

 more than half a century', there are not more than six 

 instances which may be said to have been demonstrated 

 fully. This meagre result is due to several causes, the 

 chief of which are that (i) comparatively few comets 

 revolve in orbits which intersect the earth's path or psiss 

 sufficiently near it to occasion a shower of meteors ; and 

 that (2) observational data are scanty, for students in 

 this branch of astronomy have rarely applied themselves 

 to the special purpose of discovering new instances of 

 meteoric and cometic identities. Yet if more attention 

 were directed to tliis part of the subject, there is no question 

 that our knowledge might be considerably extended. 



There are doubtless many Ctises where meteor and 

 cometary orbits e.xhibit mere chance agreements, but were 

 the observations more abundant and accurate, it would be 

 possible to select those entitled to confidence as repre- 

 senting true accordances. It is to be hoped that this 

 department will recei\-e more earnest attention in future 

 years. 



On October 22 of last year a fireball was seen at 

 Bristol and at other places by various good observers. 

 It had a long horizontal course of about 335 miles from the 

 North of England to the South of France. Its radiant point 

 was at i56°+39°. Now the comet of 1739 has a radiant 

 point at i57°-|-39° on October 22 according to computations 

 made by the late Prof. A. S. Herschel. Here is a pos- 

 sible case of a meteoric fragment from a cometarj- system. 

 The writer has seen, in and since 1877, other meteors from 

 the same source, and it seems a fair inference that these 

 objects owed their derivation to the comet named. In 

 some cases no doubt the \isible meteor showers alUed with 

 comets maj' be e.xtremely feeble, and incapable of furnish- 

 ing exhibitions of the brilliant and abundant character of 

 the Perseids of August and Leonids of November, but 

 they are none the less interesting, and deserve fuller 

 investigation. 



\V. F. Denning, F.R.A.S. 

 Bristol, 



January i6, 1920. 



Reviews of Books 



Outlines of the History of Botany. By R. J. Harvey- 

 Gibson. (Black, IDS. net.) 



Professor Harvey-Gibson has given us the substance of 

 a course of lectures wliich he delivered to his students in 

 the University of Liverpool. It is an account and a dis- 

 cussion of the more important features in the advances of 

 botanical knowledge from the earUest times down to the 

 present da}'. Now this is the kind of book we like. It 

 gives us an interest in a subject without our having to pass 

 an examination prior to our imbibing the facts. On 

 us a textbook has a stand-and-deUver eltect, but a liistory 

 is always genial and kindly. It admits us to the subject 

 at once. There is no waiting in a queue or fumbUng for 

 cash at the door. We go right in — " on the nod," it is 

 true — but we get in, and no unpleasant questions are 

 asked. 



