158 REPORTS ON THE STATE OF SCIENCE. — -1915. 



tressing in an Atlas-page, are invaluable for supplementary letterpress 

 in a wall map ; though they should never be so far filled up as to prevent 

 the map itself from standing out boldly on the sheet. 



The far larger scale of a wall map is no excuse for the introduction 

 of minute detail or a crowd of names. A wall map is essentially a 

 diagram. The use of wall maps without names, or with only a few 

 names or initials appended to town-dots or the mouths of rivers, is 

 greatly to be encouraged. Some French wall maps are printed in 

 duplicate, back to back, with the names on one side, and the physical 

 features and town-dots, unnamed, on the other. 



Even more than in the Atlas, colour shows relief better than con- 

 tours. Inclined illumination from the North-west gives, in skilful 

 hands, an almost pictorial effect. The colours of a wall map should not, 

 however, be too bright or deep, with the single exception of the scarlet 

 which is appropriately used for all kinds of arbitrary lines. 



Wall maps are o^ften too elaborate and costly. The paper must, how- 

 ever, be good enough to stand occasional cleaning with breadcrumb or 

 soft indiarubber. The use of inferior paper has led to the current 

 23ractice of varnisliing the surface. Varnish has fatal effects upon a 

 map. The reflected light from the surface makes the map useless to a 

 large class in a well-lighted room and actually diminishes the amount of 

 light from the printed and coloured surface below. There are very few 

 kinds of varnish in use which do not turn brown or yellow with age. 



It should always be remembered that the wall map is intended to 

 supplement, but not to replace, the Atlas. Most wall maps fail by 

 attempting too much. 



Gaseous Explosions. — Interim Report of the Committee, con- 

 sisting of Dr. DuGALD Clerk {Chairman) , Professor Dalby 

 (Secretary), and Professors W. A. Bone, F. W. Burstall, 

 H. L. Callendar, E. G. Coker, and H. B. Dixon, Drs. 

 R. T. Glazebrook and J. A. Harkeb, Colonel H. C. L. 

 HoLDEN, Professors B. Hopkinson ayid J. E. Petavel, 

 Captain H. Riall Sankey, Professors A. Smithells and W. 

 Watson, Mr. D. L. Chapman, and Mr. H. E. Wimperis. 

 Owing to the war, the completion of the equipment of the new 

 laboratories of the Imperial College of Science and Technology, already 

 referred to in the previous report, has been seriously delayed, and the 

 investigation of many problems of importance has had to be post- 

 poned. Also, many of the members have been engaged on work for the 

 Government, so that researches on questions under consideration have 

 been either prevented or interrupted. It is not possible, therefore, to 

 present a report to the Association this year. The general work of the 

 Committee, however, has gone on ; and during the session three meet- 

 ings were held at the City and Guilds (Engineering) College, at which 

 the following Notes were presented and discussed: — 



Note 36, by Dr. Harker, on ' A Method for the Determination of 

 the Specific Heat of the Working Fluid of a Gas Engine at High 

 Temperatures.' . • ■ 



