646 



NATURE 



[February 12, 1920 



the earth. Other geodesists consider that the devia- 

 tion is much less than this, even when the areal extent 

 is smaller; Sir S. G. Burrard, for instance, at the 

 recent discussion on isostasy before the Roval Astro- 

 nomical Society {Observatory^ December, 1919), sug- 

 gested that so small a body as the Great Pyramid 

 might be compensated. Prof. Barred, on the other 

 hand, while admitting that the larger relief of the 

 earth is compensated for with considerable exactness, 

 contends that over limited areas there are large 

 deviations — amounting' to 1000 ft. over an area 

 200 miles in diameter (about 3°), or even more. He 

 regards the upper part of the earth's crust as suffi- 

 ciently strong to sustain uncompensated loads of this 

 amount, the vertical magnitude of the departure being, 

 of course, inversely proportional to its areal extent; 

 it can thus support individual mountains or limited 

 ranges, as well as erosion features of considerable 

 magnitude,- such as the Nile and Niger deltas. Under 

 greater and more widely extended loads, however, the 

 crust is supposed to bend in gentle curves involving 

 but little crustal stress ; this bending is accompanied 

 by yielding in a lower, weaker layer, which brings 

 about isostatic compensation. 



The question at issue is largely one of fact, which 

 can be settled by observation ; e.g. if pendulum ob- 

 servations show that the Nile deposits are com- 

 pensated in the crust, the result will confirm the views 

 of ^e extreme isostasists, that continuous adjustment 

 goes on when the surface load changes over a com- 

 paratively small area. The manner of this adjustment, 

 however, lias not yet been made clear, and Prof. 

 Barren's picture of the process is more easy to con- 

 ceive. On the other hand. Sir S. G. Burrard has 

 shown recently that the alluvium in the Gangetic trough 

 at the foot of the Himalayas is compensated for. It is 

 much to be regretted that Prof. Barrel] 's death 

 deprives us of his interpretation of this result. 



DEFENSIVE SCIENCE IN GAS WARFARE. 



T^ HE prizes and certificates gained by students at- 

 -•■ the Sir John Cass Technical Institute, Aldgate, 

 were distributed by Lt.-Col. P. S. Lelean, professor 

 of hygiene, Royal Army Medical College, on the 

 evening of Tuesday, February 3, when the chair was 

 taken by the Rev. J. F. Marr, who has succeeded 

 Sir Thomas Elliott, K.C.B., as chairman of the 

 governing body. 



Following the distribution. Col. Lelean gave an 

 address on "Defensive Science in Gas Warfare," in 

 which he described the preventive measures that had 

 been adopted to meet its onset and evolution. After 

 referring to the initial attack on April 23, 1915, when 

 the civilised world was aroused to just anger by the 

 news that the Germans had broken their pledged 

 word in respect to the use of poisons as a means of 

 injuring the enemy. Col. Lelean dealt with the means 

 of protection first adopted in the form of pads soalied 

 in sodium thiosulphate, of which no fewer than 

 q8,ooo were distributed to the F'ront within sixty 

 hours of the attack, 300,000 within a week, and 

 2,000,000 within a month — a truly notable achieve- 

 ment, which was rendered possible only bv the com- 

 bined efforts of men of science, manufacturers, and 

 voluntary helpers. 



With the recognition of gas attacks as an estab- 

 lished adjunct of modern warfare, this temporarv 

 device was succeeded by the more efficient protective 

 appliances which were called for by the advent of 

 toxic, paralysing, and lachrymatorv gases such as 

 carbonyl chloride, hydrocyanic acid,' and chloropicrin, 

 which culminated first in the adoption of the "P" 

 helmet, of which nearly 27,ooo,(X)o were issued 

 NO. 2624, VOL. 104] 



between July, 1915, and ,the final withdrawal in 

 February, 1918, in favour of the now well-known 

 "box-respirator." 



A full description was given of the great difficulties 

 that were met with stage by stage during the develop- 

 ment of these protective appliances, especially in 

 respect to the need for the complete absorption of the 

 small percentages of the poison gases concerned, 

 together with the fundamental requirements of com- 

 parative ease of breathing anA exhalation. 



Col. Lelean paid a special tribute to the outstanding 

 services of Sir William Horrocks and to the late Col. 

 E. F. Harrison in this connection ; also to the many 

 scientific helpers with whom they were associated, 

 and particularly to the gallantry and devotion to dutv 

 of the small band of scientific workers who had served 

 under him and upon whom had devolved the practical 

 testing of the efficiency of the many devices whicli 

 were experimented with in a "lethal chamber" before 

 their issue to the fighting forces could be justified. 



In speaking of tlie helpful war-work contributed 

 bv the staff of the Sir John Cass Technical Institute, 

 Col. Lelean expressed the view that it was to such 

 institutes that the nation looked in its hour of scientific 

 need, and had not looked in vain ; and that it is to 

 such institutes also that, with an ever-increasing 

 appeal, we shall have to look for victorv in the future 

 strife of industrial competition, which can be won onlv 

 bv suoerior technical skill. 



VISUAL TESTS FOR MOTOR-DRIVERS. 



'T'HE Council of British Ophthalmologists, realising 

 -*■ the importance of submitting chauffeurs and 

 other drivers of motor vehicles to some visual tests, 

 appointed a committee to consider the question. Its 

 report is divided into five parts : — (i) The existing 

 conditions under which licences are at present granted ; 

 (2) the number of accidents occasioned annually in 

 London by mechanically propelled vehicles ; (3) the 

 various kinds of visual defects in motor-drivers from 

 which accidents may arise; (4) proposed scheme of 

 visual testing for licences ; and (5) summary of 

 recommendations. The subject is complicated bv the 

 following facts. There are two licensing authorities, 

 the county or borough councils and the police authori- 

 ties. The requirements vary according to the type of 

 vehicle, e.g. private cars, commercial cars, omni- 

 buses, taxi-cabs, and tramcars. The total number of 

 applicants for licences mal<es it impracticable .to 

 submit every one to a satisfactory sight test. The 

 council's cliief recommendations arc : — 



"Tliat special sight-test certificates for drivers of 

 motor vehicles be instituted, and granted to applicants 

 whose sight has been tested by ophthalmic surgeons 

 appointed for the purpose, these certificates to be of 

 tliree grades : Grade A, certifying the holder's visual 

 capacity to drive any kind of motor vehicle ; Grade B, 

 certifying the holder's visual capacity to drive any kind 

 of motor vehicle other than a motor-omnibus or 

 tramcar; and Grade C, certifying the holder's visual 

 capacity to drive a motor-tramcar. 



" For Grade A Certificate. — (i) Every applicant, '.n.i 

 addition to manifesting his abilitv to steer a motor-car j 

 satisfactorily in dayliglit, should be required, in a] 

 trial trip at night, to sliow himself capable of drivingj 

 in dim light and under varying degrees of illumina-| 

 tion. (2) In an examination by an ophthalmic surgeonl 

 he should show : (a) Visual acuity of 6/9 in one eye| 

 and 6/24 in the other eye without the aid of glasses;! 

 (b) a full field of vision in each eye; (c) no manifest] 

 squint; and (d) no double vision. 



" For Grade B Certificate. — (i) Every applicant, inJ 

 addition to manifesting his ability to steer a motor-carl 



