SECTIONAL TRANSACTIONS.— G. 587 



the first practical solution of the problem of mechanical rectification of high powers. 



Other applications of the synchronous jet-wave are the jet-wave frequency-meler 

 and the jei-tvave conlact-maker, a substitute of the Joubert-disk for the point-in-point 

 determination of a.c. waves. 



Finally the wave producrti by an arbitrary current may be used in the jet-wave 

 oscillograph for obtaining oscillograms of the current in question. For the motion 

 of the point of intersection between the wave and a plane perpendicular to the original 

 jet is conform to the current producing the wave. The new oscillograph has practically 

 the same sensibility as a modern Duddell oscillograph. 



Mr. J. G. DocHERTY. — The Effect of the Velocity of Test on the Notch 

 Brittleness of Mild Steel and Other Metals. 



The author first refers to some of the published results of notched bar bending 

 tests, and points out the lack of agreement as to the nature of the velocity effect. 

 The object of liis experiments is to investigate this effect more fully by carrying out 

 tests at a number of speeds, in the hope that the results obtained will throw some 

 light on the discrepancies between the results of other experimenters. The experi- 

 ments are not yet complete, but some interesting results have already been obtained. 



The testing gear is designed to reproduce, as closely as possible, the characteristics 

 of the Izod test on the standard 10 mm.x 10 mm. notched specimen. The energy 

 absorbed in bending or breaking the specimen is recorded autographically. The 

 speed of the ' striker ' can be varied as desired, and in the experiments described 

 ranged from 0-05 in./min. to 50 in./min. The standard Izod test speed is about 

 7,000 in./min. 



The most complete series of tests was made on mild steel. The energy absorbed 

 is shovni to increase with speed of testing, the Izod figure lying somewhat above a 

 smooth curve passing through the slow bend results. 



Tests were also made on nickel steel and naval brass. In the former the energy 

 increases slightly with speed of test up to the fastest slow bend test, but the Izod 

 figure is about 50 per cent, lower. In naval brass, the energy absorbed increases with 

 speed, up to the Izod value. 



Observations made during the tests indicate that the propagation of the fracture 

 is not continuous, but intermittent, as if by alternate rapid cracking and slower 

 ductile tearing. It is suggested that the anomalous result in the case of nickel steel 

 may be due to the existence of a critical speed, above which the cracking effect pre- 

 dominates, with consequent diminution of energy absorbed, and that in nickel steel 

 this critical speed lies below the speed of the Izod test, while in mild steel and naval 

 brass it lies above. 



In addition, a series of photographs is shown, tracing the development of the 

 fracture in a mild steel specimen. 



Prof. A. P. Thurston. — The Control of Aircraft by Supplementary Airettes 

 or Alulas. 



Afternoon. 



Visit to Greenock (Works of Messrs. John Kincaid & Co., R.N. Torpedo 

 Factory, Watt Library and Engineering School). 



Wednesday, September 12. 



Report of Committee on Electrical Terms and Definitions : Papers by 

 Prof. G. W. 0. Howe, Prof. C. L. Fortescue, and Prof. E.W. Marchant. 



Report of Committee on Earth Pressures. 



