668 



SCIENCE. 



[N. S. Vol. V. No. 121. 



It was shown to be possible to perform any 

 operation of plane perspective with a sliding 

 linkage of three rods and by a slight modifica- 

 tion of the pantagraph to obtain any desired 

 orthogonal or parallel projection of an irregular 

 figure or surface. 



The author also called attention to the 

 extreme simplicity of the methods of project- 

 ing extensive panoramic views from contoured 

 maps by the employment of a linkage of two 

 threads, the methods being fully illustrated by 

 the drawings and models accompanying the 

 paper. 



2. ' The Nerve Impulse in its Relations to 

 the Strength of the External Stimulus,' by C. 

 W. Greene. 



The papers presented and read by title 

 were : 



1. 'A New Form of Mirror for Reflecting 

 Tielescopes, ' by Chas. Lane Poor. 



The mirror is a portion of a paraboloid of 

 revolution, cut at the extremity of the param- 

 eter. The advantages over the old form were 

 indicated as follows : Utilization of the full 

 aperture ; the reflected beam being at right 

 angles to the incident light ; no second mirror 

 necessary ; possibility of constructing mirrors of 

 great focal length ; possibility of such mirrors 

 of short focal length, replacing photographic 

 doubts. 



2. 'A New Form of Equatorial Mounting for 

 Reflecting Telescopes.' 



With mirror of the above form an equa- 

 torial mounting becomes very simple ; the dec- 

 lination axis becomes the telescope tube, the 

 mirror being mounted at extremity of such 

 axis and capable of revolving about it in a 

 manner similar to the large flat of the equa- 

 torial cond6. 



The image is formed at the intersection of 

 the polar and declination axes and is always in 

 the same position; the observer, therefore, re- 

 mains at rest while viewing any and every 

 part of the visible heavens. A single reflecting 

 surface replaces three in the reflecting equatorial 

 cond6, and four in the forms mentioned by 

 Wardsworth. No dome is required. Many 

 other advantages were indicated and several 

 modifications of the general form pointed out. 



Note. — Experiments with mirrors of the 



above form are now being carried out at the 

 University. Chas. Lane Poor, 



Secretary. 



BIOLOGICAL SOCIETY OF WASHINGTON, 274TH 

 MEETING, SATURDAY, MARCH 27TH. 



Mr. M. B. Waite spoke on ' Factors Govern- 

 ing Pear Blight,' showing that the very condi- 

 tions which were favorable to the growth of the 

 tree were also favorable to the development of 

 the disease, and that an important factor in 

 combating the blight was the prevalence of a 

 considerable degree of drouth. 



Mr. Theo. Holm gave a historical review of 

 our knowledge of ' The Grass Embryo and its 

 Constituents.' He described the embryo as 

 defined by Malpighi and authors of recent date, 

 saying that there seemed to be good reason for 

 adopting the explanation of its structure given 

 by Malpighi more than 200 years ago. This 

 involves the definition of both the ' scutellum ' 

 and the 'lobule' as independent leaves, while 

 the 'pileole' thus becomes the first sheathing leaf 

 or the second leaf proper after the cotyledon. 

 A full account will soon appear in an article 

 upon Fuirena, by the speaker, in the American, 

 Journal of Science. 



Dr. E. A. De Schweinitz described ' Some 

 Methods of Generating Formaldehyde and its 

 use as a Disinfectant,' showing a specially de- 

 vised form of lamp with a platinized wick by 

 which large volumes of the gas could be readily 

 generated. F. A. LucAS, 



Secretary. 



NEW BOOKS. 



The Materials of Construction. J. B. JoHNSON. 

 New York, John Wiley & Sons. 1897. Pp. 

 XV + 787. $6.00. 



The Principles of Mathematical Chemistry. Geo. 

 Helm. Authorized translation from the Ger- 

 man by J. Livingston R. Morgan. New 

 York, John Wiley & Sons. 1897. Pp. viii+ 

 228. $1.50. 



An Outline of the Theory of Solution. J. Liv- 

 ingston R. Morgan. New York. 



Plane and Solid Analytical Geometry. Freder- 

 ick H. Bailey, Frederick S. Woods. 

 Boston and London, Ginn & Co. 1897. Pp. 

 xii+871. 



