228 Geological Society: — 



seems to add one more to the many indications that the Pacific 

 coast throughout North America, if not throughout the two 

 Americas, has had a very similar history." 



The Photochronograph and its Application to Star-Transits. By 

 J. G-. Hagen, S.J. (Stormont & Jackson, Printers, Washington, 

 D.C.: 1891.) 

 This is a pamphlet of 36 pages and 2 plates describing experi- 

 ments and results in photographing star-transits at the Georgetown 

 College Observatory. The work had its origin in a visit made by 

 Prof. P. Bigelow and Mr. Gr. Saegmiiller to the Observatory named 

 in the summer of 1889, and it is confidently stated that "this 

 method of letting the sensitive plate take the place of the eye and 

 the chronograph seems to have a great future." It is claimed that 

 the entire absence of personal equation in the results, and the fact 

 that the probable errors are smaller than in the usual plan, give to 

 the photographic method a practical importance and superiority 

 which cannot fail to be recognized. "A photographic transit is, on 

 the whole, more laborious than one taken by the chronograph, yet 

 it certainly makes it possible for us to eliminate the personal equa- 

 tion in all cases where such elimination must be purchased at any 

 cost. As an example we need only mention longitude determina- 

 tions. The usual exchange of the observers, so expensive in time 

 and money, is, by the photographic method, rendered unnecessary 

 and even useless. If the photochronographs at the two stations 

 are worked by the same clock at either station, or at an intermediate 

 one, the sensitive plates will record the difference of the two meri- 

 dians without the interference of the observers." The experiments 

 are to be continued, the peculiar errors of the method are to be 

 studied, and it is proposed to test its efficiency in regular zone 

 work. 



XXXI. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 



[Continued from p. 141.] 



June 24, 1891.— Sir Archibald Geikie, D.Sc.,LL.D.,P.B.S., President, 



in the Chair. 



THE following communications were read : — 

 1. " On Wells in West-Suffolk Boulder-clay." By the Rev. 

 Edwin Hill, M.A., F.G.S. 



It might be supposed that in a Boulder-clay district water could 

 only be obtained from above or from below the clay. But in the 

 writer's neighbourhood the depths of the wells are extremely 

 different, even within very short distances ; and since the clay 

 itself is impervious to water, he concludes that it must include 

 within its mass pervious beds or seams of some different material 

 which communicate with the surface. It would follow that this 

 Boulder-clay is not a uniform or a homogeneous mass. 



