676 Intelligence and Miscellaneous Articles. 



will present but little difficulty to any reader who has had the 

 advantage of a good general education. The little volume into 

 which the author has compressed so much interesting information 

 forms No. 28 of the physico-mathematical section of the well- 

 known series published under the general title of " Scientia." 



LXVI. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 



[Continued from p. 556.] 



June 5th, 1907.— Sir Archibald Geikie, D.C.L., Sc.D., Sec.B.S., 

 President, iu the Chair. 

 r PHE following communications were read : — 



1. 'A Marine Fauna in the Basement-Beds of the Bristol Coal- 

 field/ By Herbert Bolton, F.H.S.E., F.G.S. 



2. ' Brachiopod Morphology : Cincta, Eadesia, and the Develop- 

 ment of Bibs.' By S. S. Buckman, F.G.S. 



LXVII. Intelligence and Miscellaneous Articles. 



To the Editors of the Philosophical Magazine. 



GrENTLEMEN, 



MAT I be allowed to remind the writer of a paper appearing at 

 p. 395, Phil. Mag. 1907, the title of which is " Experimental 

 Mathematics " by Mr, E. A. K Pochin, B.A., that the instrument 

 employed by him for drawing logarithmic spirals is not quite so 

 new as he supposes. One instrument for drawing the Logarithmic 

 curve was made from my designs in 1891 for use in the Millard 

 Mechanical Laboratory, Oxford. Another was added to the 

 collection of apparatus in the Physical Laboratory. Winchester 

 College. And a paper was read at the B.A. Meeting at Edinburgh in 

 1892 on asomewhat similar contrivance, where diagrams were shown. 

 The tracing wheel is best kept upright, by means of two equal 

 links, similar to those employed in my linkage integrator of 1884. 

 The tractrix can also be easily drawn by another simple application 

 of the tangent wheel. It is found convenient in my logarithmic 

 curve drawer, to produce the radius bar beyond the tangent 

 wheel, so that the angle swept out may be measured at once on a 

 divided circle, the radius bar when graduated indicating the 

 length from the point of contact of the tangent wheel to the 

 point about which the radius bar moves, for the angle swept out 

 by it. Mr. Pochin urges that diagrams, models, and actual 

 measurements should be used in laboratory teaching. It was 

 exactly for this purpose that the original 1891 instrument was 

 designed by me, for drawing the logarithmic curve and showing 

 its properties to my students. 

 Millard Laboratory, Oxford, Yours faithfully, 



Sept. 6, 1907. F. J. Jebvis -Smith. 



