362 SECTIONAL TRANSACTIONS.— G. 



(i) From each phase of a lighting transformer fed from the power mains 

 a series circuit is connected between phase and neutral, the neutral wire 

 being earthed. 



(2) In each such circuit the primaries of a number of special transformers 

 are connected in series without switches. The secondary of each trans- 

 former feeds one lamp in an appropriate fitting. 



(3) The transformers are constructed so that the lamp, tail, secondary 

 and yoke can easily be withdrawn as one unit ; and this is the method of 

 extinguishing or removing a lamp. 



(4) The characteristics of the transformers are such that no matter 

 whether a lamp be in place, withdrawn, or even short-circuited, the primary 

 circuit is not substantially disturbed. 



(5) The most vulnerable portion of the circuit then becomes the lamp. 

 It is proposed to use a fitting provided with a glass which will withstand 

 the shock of an explosion or of shot-firing, in which case the secondary 

 voltage would be either 12 or 25. If this is not considered satisfactory, 

 recourse can be had to the special lamp recently designed by Dr. Wheeler. 



The advantages of the system are : simplicity of connection, low voltage 

 on each primary and each secondary, and the removal or extinction of any 

 lamp without opening a switch and with no risk. 



Mr. J. Gilchrist and Dr. R. H. Evans. — Elasticity and hysteresis of rocks 

 and artificial stone. 



In this paper is described a new method of investigating the elastic 

 properties of rocks, part of which consists in allowing a column of the 

 material to stand for a long time under a given load, and then to vary this 

 through a small range. The strain so obtained is termed the short range 

 strain, from which we can calculate the short range modulus. In general, 

 for stone and concrete, the short range strain decreases with increasing load, 

 and the modulus increases. This short range strain, with certain limitations 

 for concrete, is a constant magnitude found always on returning to the same 

 average load ; it is independent of time. The sum of the short range 

 strains integrated between two given loads differs from the actual strain 

 obtained when observations are made in the ordinary manner. The 

 difference between this integral short range strain and the actual strain is 

 a time eifect. The authors suggest that this conception of a short range 

 strain combined with the time effect gives clearer ideas of the stress-strain 

 relations of the materials in question. For example, the elastic hysteresis 

 loop can be explained in terms of these two effects. 



Afternoon. 



Visit to L.N.E.R. Carriage Works, Signalling School and Museum, 

 York. 



Wednesday, September 7. 



Prof. F. Bacon. — Cracking and fracture in rotary bending tests. 



The primary aim of the experiments described has been to reproduce in 

 laboratory tests the features found on the fractured faces of rolls, shafts 

 and axles which have failed in service by the gradual spreading of cracks. 

 The investigation arose from the desire to interpret the various markings 

 of simple geometric form often found on the freshly fractured faces of the 

 chilled iron rolls used in the hot mills of sheet and tinplate works. 



