830 



SCIENCE 



[N. S. Vol. XLIL No. 1093 



Miss Gertrude I. McCain lias been ap- 

 pointed professor of mathematics in tlie West- 

 ern College for Women, Oxford, Ohio. 



DISCUSSION AND COSBESPONDENCE 



A REMARKABLE ECLIPSE 



To THE Editor of Science: Eclipses of the 

 sun and moon occur with such frequency and 

 are so similar in character and appearance that 

 a distinction between them sufficiently great 

 to be noticed by the uncritical observer would 

 seem to be out of the question. The cause of 

 eclipses is well known, and as they may be 

 easily calculated the times of their occurrence 

 and nature of their appearance are always pub- 

 lished in the INautical Almanac two or three 

 years before they actually take place. Total 

 eclipses of the sun have for many years afforded 

 the necessary darkness for observing the heav- 

 ens in close proximity to the sun; and numer- 

 ous expeditions have been sent to distant parts 

 of the earth in order to take advantage of the 

 few moments of additional darkness thus 

 afforded; and much interesting and useful 

 information concerning the physical constitu- 

 tion of the sun has been obtained in this man- 

 ner. At the present time, however, the chief 

 importance of eclipses lies in the opportunities 

 they afford for testing the accuracy of the cal- 

 culations of mathematicians, and the correct- 

 ness of the physical theories on which such 

 calculations are based; and for this purpose 

 the distinction between partial and total 

 eclipses is of little importance. 



In the year 1915 there were only two eclipses, 

 both of the sun. The first occurred on Feb- 

 ruary 13 Tuider ordinary circumstances; the 

 central eclipse began at sunrise in the Indian 

 Ocean a few degrees to the southward of the 

 island of Madagascar ; passing along the north- 

 western coast of Australia, it crossed the island 

 of "New Guinea and ended at sunset in the 

 ISTorth Pacific Ocean. The second eclipse took 

 place on August 10; beginning at sunrise a 

 few degrees to the southward of the Japanese 

 Islands in the North Pacific Ocean. It moved 

 to the eastward a few degrees southward of the 

 Sandwich Islands at noon, and ended at sun- 

 set in the South Pacific Ocean. These two 



eclipses were very similar in character in so 

 far as outward appearances are concerned. 

 Their relative importance arises from the very 

 dissimilar conditions imder which they took 

 place. In the eclipse of August 10 the 

 centers of the sun, moon and earth were very 

 nearly in the same straight line. I have ex- 

 amined the record of all the eclipses that have 

 taken place since the year 1767; and I find 

 that in the year 1903 there were two very sim- 

 ilar eclipses; one of which took place on Feb- 

 ruary 21 and the other on August 17 of that 

 year. 



It has, therefore, been one hundred and twelve 

 years since a similar eclipse happened; and I 

 find that the next similar eclipse will occur on 

 July 11, 1991, or seventy-six years from the 

 present time. It is, therefore, only on very 

 rare occasions that such eclipses take place and 

 this fact seems worthy of mention in the his- 

 torical record of important eclipses. 



It may, however, interest the reader to know 

 how or why I happened to make this important 

 discovery, as it has been many years since I 

 was engaged in the discussion of eclipses for 

 chronological purposes. I will, therefore, give 

 a brief account of my investigations which so 

 happily led to this discovery. 



In the early summer of the year 1906 I was 

 much embarrassed by a superfluity of leisure, 

 and unable to pass my time agreeably with 

 nothing to do. I had then recently been read- 

 ing G. H. Darwin's interesting book on " The 

 Tides and Kindred Phenomena," and learned 

 that the mathematical theory of the tides was 

 in a very unsatisfactory condition. I had read 

 in my yoimger days the explanations of the 

 tides by Newton and by Laplace. These ex- 

 planations seemed so plausible that I then ac- 

 cepted them as correct. But as I had devoted 

 the greater part of my life to the discussion 

 of gravitational problems, the thought occurred 

 to me that possibly a new discussion of an old 

 problem might throw additional light upon a 

 subject which was confessedly very obscure. 

 I therefore concluded to undertake a critical 

 discussion of the theory of the tides, and the 

 discovery of the remarkable eclipse came as a 

 bi-product of that discussion. My leisure has 



