l8o PROCEEDINGS: PHILOSOPHICAL SOCIETY 



823D MEETING 



The 823d meeting was held at the Cosmos Club, November 8, 19 19, 

 with President Humphreys in the chair, and 55 persons present. 



R. W. G. Wyckoff: The nature of the forces between atoms in solids . 



This paper, which has since been published in this Journal (9: 565. 

 Nov. 19, 19 19) was illustrated by lantern shdes and discussed by Messrs. 

 Sosman, White, Humphreys and Bray. 



H. L. Curtis, R. C. Duncan and H. H. Moore: Methods of mea- 

 suring ballistic phenomena on a battleship. The paper was presented 

 by Mr. Curtis. 



In 191 7, apparatus was designed for obtaining the relative time of 

 ejections of the three shells, when the three guns of one turret of a battle- 

 ship were fired simultaneously. The method consisted in having a 

 condenser charged to a high potential and circuits so arranged that 

 when the shell emerged from the gun it short-circuited two wires which 

 were stretched in front of the gun, thus completing the electric circuit 

 and discharging the condenser through a point on a chronograph drum. 

 The method was satisfactory although the spark which was produced 

 was not as vigorous as had been expected. Tt was later shown that this 

 was caused by the discharge taking place through the hot ionized gas 

 which preceded the shell. This, however, did not appreciably affect 

 the results, since approximately the same interval existed in all the 

 guns. 



It was soon found advisable to use a method which would be more 

 flexible than the spark method outlined above. After careful considera- 

 tion of the possible methods available, it was decided to use an oscillo- 

 graph as a timing instrument. An oscillograph is simply a galvanometer 

 of very high period which is critically damped, and which is arranged 

 for photographing the movements of the mirror on a moving film. 

 Three of these galvanometers or oscillograph elements are usually 

 mounted in one instrument, all giving records on one film. To use this 

 for timing various events, it is simply necessary to arrange an electric 

 circuit in such a way that the events will produce a change in the elec- 

 tric circuit through the oscillograph element, thus causing a deflection 

 of the mirror of the oscillograph element which is registered on the 

 photographic film. It is also necessary to know the velocity of the 

 film. 



To obtain the velocity of the film, a tuning fork having small plates 

 on the prongs is employed. When the tuning fork is at rest, a fine slit 

 is cut through the two plates. The tuning fork is then mounted so 

 that a beam of light passes through this slit and makes a line on the 

 film when both the fork and the film are at rest. If now the fork vi- 

 brates and the film is in motion, lines will be produced on the film giving 

 an accurate record of the velocity of the film. This method has already 

 been described in a paper before the Society.' 



The above method has been used to obtain with a single oscillograph 



1 Meeting of May 24, 1919, abstracted in this Journal, 9: 642., Dec. 4, 1919- 



