38 JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOL. 11, NO. 2 



On the Pacific coast somewhat similar conditions obtain. The currents 

 close inshore are of the rectilinear type, while those offshore are of the clock- 

 wise rotary type. However, the two current curves of a tidal day are gen- 

 erally quite different. This is due to the diurnal inequality present in the 

 tides of the Pacific coast. 



The diurnal inequality is largely a function of the moon's declination. 

 It therefore varies throughout the month, being at a minimum when the 

 moon is on the equator and a maximum when the moon is furthest north 

 or south. The effect of this on the rotary current is to make the two cir- 

 cuits of a tidal day very nearly alike when the moon is on the equator, but 

 quite unlike when the moon is farthest north or south. 



The paper was illustrated with lantern slides, and was discussed by Messrs. 

 White, C. A. Briggs, Tuckerman, O. S. Adams, Humphreys, Beall, 

 McKeehan, Bowie and Hawkesworth. 



In reply to questions by Messrs. White, Humphreys and Adams, it 

 was brought out that the relation of strength of current to time of high 

 and low^ water varies greatly; that the motion of tidal currents is in the 

 same direction from surface to bottom, and that the direction of rotation 

 of the rotary current is conditioned by local causes. 



S3GTH meeting 



The S36th meeting was held at the Cosmos Club, May S, 1920, with 

 President Sosman presiding and 30 persons present. The program was as 

 follows : 



F. B. Silsbee: Physics of the high-tension magneto. 



Magnetos for igniting internal combustion engines have been gradually 

 evolved in parallel with the development of the engines on which they are 

 used, and the present high-speed, high-compression engines have led to the 

 development of the present so-called "high-tension magneto." This is an 

 extremely complex electrical system and the complete details of its opera- 

 tion are relatively little understood even by the manufacturers of the ap- 

 paratus. 



The speaker described the results of a study of this type of device carried 

 out at the Bureau of Standards in connection with the developing and test- 

 ing of aircraft engines. The results of this study have been published in 

 Report No. 58 of the National Advisory Committee for Aeronautics. 



The cycle operations of the magneto can be divided into a number of 

 periods during each of which the electrical phenomena proceed under fairly 

 definite conditions, but each of which is separated from the one preceding 

 and the one following it by a change of conditions, such as the opening of 

 the primary contact or the breaking down of the spark gap. Some of 

 these periods, such as the building up of the primary current can be studied 

 by means of the oscillograph, but others, such as the rise of voltage after 

 "break" are so short that this instrument cannot record the phenomena. 



The paper was illustrated by a number of oscillograms showing both 

 normal and abnormal performance of ignition apparatus. 



Discussion: The paper was discussed by Messrs. C. A. Briggs, White, 

 Sligh and Sosman. 



C. Nusbaum: The magnetic reluctivity relationship as related to certain 

 structures of an eutectoid carbon steel. 



The magnetic reluctivity p, defined as the ratio of the magnetizing force 

 to the induction, has been shown by Kennelly to be related to the magnetizing 

 force by the relationship 



