December 29, 1923] 



NA TURE 



953 



it ; in this is a slit, parallel to that in the surface | 

 of the inner cylinder, while outside this slit, and in- 

 sulated from the cylinder, is a collecting plate, which 

 receives the electrons which pass through both slits. 

 The inner cylinder can be rotated about its axis ; so 

 that the angle between the planes passing through 

 either slit and the cathode wire can be varied, and 

 measured by means of a reflecting mirror. A solenoid 

 is wound round the cylindrical glass containing 

 vessel, so that a magnetic field can be produced in the 

 direction of the axis of the cylinders, deflecting 

 electrons with a certain velocity which pass through 

 the first slit, so that they pass through the second 

 when (t> has the correct value. Maxwell's law is still 

 found to hold. 



Magnetic Survey of the Balkans. — Heft 10, Bd. 

 131, Abt. Ha, Math. Nat. Kl. of the Sitzungsberichte 

 of the Vienna Akademie der Wissenschaften contains 

 a paper by Mr. A. Schedler, which gives the results of 

 a magnetic survey carried out during 191 8 in the 

 Balkans. Results are given for 27 stations, varying 

 in latitude from 44° 49' to 40° 55' N., and in longitude 

 from 18° 32' to 21° 55' E. Attached to the paper are 

 six charts. The first and the last indicate the geo- 

 graphical positions of the stations, and the geological 

 features of a magnetically disturbed region. The 

 four intermediate charts give curves of equal values 

 of magnetic declination, inclination, horizontal force, 

 and total force respectively for the epoch January i, 

 191 8. Through an oversight, the values of the force 

 are printed as angles in the charts. For example, 

 0-4444 C.G.S. is printed as 44° 44'. It is interesting to 

 note that the dip observations were taken with an 

 English dip circle, Dover No. i. 



Inverted Flight in Aeroplanes. — A paper of 

 considerable interest to practical aviators, as well as 

 to workers in the dynamics of aeroplane flight, was 

 read recently before the Royal Aeronautical Society 

 by Squadron Leader R. M. Hill. The paper is en- 

 titled " The Manoeuvres of Inverted Flight," and is 

 based upon extensive experimental flights executed 

 by Mr. Hill and others. The object of the experiments 

 was threefold. The immediate aim was to examine 

 the causes of fatal accidents that often occur in 

 aerobatics on an unstable aeroplane, when the aero- 

 plane assumes an inverted position and the pilot fails 

 to right the machine. Subsidiary aims were to find 

 the magnitudes of the loads in inverted flight, and to 

 examine the behaviour in inverted flight of machines 

 with different stability characteristics. An account 

 is given of the ways in which inverted flight can be 

 obtained, namely, by means of the half loop and the 

 half roll, and details of the manoeuvres are given for 

 particular aeroplanes, such as the Sopwith " Camel," 

 the " Camel " modified so as to increase its longitudinal 

 stability, the " Snipe," the " Bat Bantam," and the 

 S.E.5A. The use of the controls in inverted flight and 

 the return to normal flight are similarly discussed. 

 Mr. Hill considers the belting arrangements to be of 

 supreme importance, especially in unstable fighting 

 machines ; pilots often fail to use the controls because 

 they cannot reach them. Steady inverted flight is 

 possible on all types of machines investigated ; but 

 whereas the longitudinally stable machine tends to 

 right itself, the longitudinally unstable machine has 

 no such self-righting properties : there is, however, no 

 real difficulty in recovering from the inverted flight. 

 The longitudinally unstable machine is also liable to 

 get into an inverted spin, but here again the pilot can 

 recover if he knows the use of the controls in such 

 positions. Inverted loops were also investigated. 

 Mr. Hill suggests that " tne best compromise between 



NO. 2826, VOL. I 12] 



safety and extreme manoeuvrability is to be found in 

 an aeroplane which, though preferably stable through- 

 out the major part of its range of flying speeds with 

 elevators free, must definitely be stable with them 

 fixed." 



Silicate of Soda for the Treatment of Concrete 

 Roads. — Silicate of soda is now being more and more 

 used in Great Britain for the surface treatment of 

 concrete, following on the extensive and very satis- 

 factory experience recorded in America. In fact, 

 new uses for silica of soda are being found almost 

 every day, and this material looks like rivalling 

 sulphuric acid, soap, or soda ash as a ready test, 

 according to the amount consumed, for the civilisation 

 of a community. The chemical reactions that result 

 from the application of a dilute solution of silicate 

 of soda to concrete, say the surface of a road, are 

 very complicated, but seem to include the combination 

 of the silicate with the free hydrated lime liberated in 

 the setting of cement to give a lime silicate, which 

 forms a hard compound. At any rate, the nett result 

 is the formation of an intensely hard outer skin — in 

 which all the pores have been completely filled up — 

 strongly resistant to abrasion and dusting, and 

 largely waterproof. It is essential, however, that the 

 silicate of soda be sprayed over the road in the form 

 of a very dilute solution, say i of the liquid neutral 

 silicate to 4 of water, whilst the silicate of soda must 

 be prepared for the specific purpose, with a fairly 

 high ratio of silicate to soda. As is well known, 

 very many grades are supplied, from a low-ratio 

 product containing i-6o molecules silica to i-oo 

 molecules soda (NagO) to a very high-ratio grade with 

 over 4-0 molecules silica. The right brand to use is 

 a matter of experience and research on the part of 

 the firms supplying the product, but the results, 

 under proper conditions, are remarkable, and con- 

 stitute a factor of national importance in the upkeep 

 of roads. 



Tests on Boiler Material. — The annual memor- 

 andum by Mr. C. E. Stromeyer, Chief Engineer to 

 the Manchester Steam Users' Association, covering 

 the year 1922, contains several interesting matters. 

 Tests have been made on the material of .some old 

 wrought-iron boilers, one of which was sixty-nine 

 years old, and a comparison with the tests of the 

 original material shows that wrought iron does not 

 lose tenacity appreciably with age. The furnace 

 plates show a reduction of ductility, but not of tenacity. 

 Mr. Stromeyer again directs attention to the effect 

 of nitrogen- on mild steel, and urges that the effect 

 of a high proportion of this element, such as is found 

 in Bessemer steel, requires more thorough investiga- 

 tion. A table of failures of mild-steel plates, bolts, 

 stays, and rivets is given, 22 in number, and in 

 every case the sum of 5N4-P is greater than o-oS 

 per cent., the upper limit previously fixed by the 

 author. A case for inquiry has been made out, 

 and it is to be desired that analyses for nitrogen 

 should be made more frequently, until its alleged 

 harmfulness has been confirmed or disproved. The 

 tests on riveted joints in old boilers show that the 

 strength of a double-riveted seam in a boiler is greater 

 than that found when the seam is cut out and the 

 joint tested in a machine, so that the engineering 

 practice of crediting the joints with their full strength 

 is justified. An interesting section on dished and 

 flat-end plates of boilers deals with the behaviour 

 of cracks, which in some cases do not spread, but 

 relieve the stress, so that some boilers mentioned 

 worked for years in a cracked condition. This is 

 traced to a very finely laminated structure in the 

 outer layers of the plates. 



