454 



SCIENCE 



[Vol. IV., No. 



a different denominator. It is, in the present nota- 

 tion, 



. = 2 (ag)(6 6)-(ai)(6a) 



j (ua) + (aft) + (ba) + (bb) j 2 - («a) 2 + (a&) 2 + (6a) 2 - (66)2' 



For Sergeant Finley's tornado-predictions, (aa)^ 

 28, (ab)=72, (6a)=23, (66)=2,680. From these data, 

 Mr. Gilbert finds i = 0.216, while my formula gives 

 i = 0.523. 



If the questions should present more than two alter- 

 natives, it would be necessary to assign relative values 

 or measures to the different kinds of mistakes that 

 might be made. I have a solution for this case. 



Another problem is to measure the utility of the 

 method of prediction. For this purpose, let p be 

 the profit, or saving, from predicting a tornado, and let 

 / be the loss from every unfulfilled prediction of a 

 tornado (outlay in preparing for it, etc.); then the 

 average profit per prediction would be, 

 p . {act) — I ( ab) 

 (act) + {ab) + {ba) + (bb)' 



C. S. Peirce. 



Measurement of the speed of photographic 

 drop-shutters. 



The usual method adopted for this purpose de- 

 pends on photographing a white clock-hand revolv- 

 ing rapidly in front of a black face. 1 The chief 

 difficulty in this case is to maintain a uniform rota- 

 tion at high speed. To avoid this difficulty, and to 

 determine the uniformity of exposure of any par- 

 ticular shutter under apparently like circumstances, 

 the following method has been suggested. In carry- 

 ing out the experiment in practice, I have had the 

 assistance of Mr. J. O. Ellinger. 



A tuning-fork, B, with a mirror attached to the side 

 of one of the prongs, is placed in front of the camera- 

 lens. This mirror is so arranged as to reflect into the 

 camera, C, a horizontal beam of sunlight, which, before 

 reaching the fork, has passed through a half-inch 

 hole in a screen, 8, placed about ten feet distant. This 

 produces on the ground-glass a minute brilliant point 

 of light. If the fork be set vibrating, the point will 

 become a short, fine, horizontal line : if the fork be 

 rotated about its longitudinal axis, the line will be- 

 come a sinusoidal curve described on the circum- 

 ference of a circle of long radius. A photographic 

 plate is now inserted, and the drop-shutter attached. 

 On releasing the latter, it will be found that a portion 

 of the sinusoid has been photographed; and the pre- 

 cise exposure may be determined by counting the 

 number of vibrations represented on the plate. 



The mirror employed should be somewhat larger 

 than the lens to be measured, so as to cover its edges 

 during the whole exposure. The mirror may be glued 

 directly to the prong 01 the fork with strong carpen- 

 ter's glue, after first scraping off a little of the silver- 

 ing at the edges of the glass. The rate of the fork 

 is then determined, by comparison with a standard 

 fork, by the method of beats. W. H. Pickering. 



Photographic laboratory, 

 Mass. hist, of technology. 



1 For other method*-, sec Brit, journ. photography, Aug. 31, 

 1883, and May '23, 1884. 



THE IMPORTANCE OF CHEMISTRY IN 

 BIOLOGY AND MEDICINE. 



The position of chemistry in the biological 

 sciences has long been, in English-speaking 

 communities, a very indefinite one : in fact, 

 it may be questioned whether the science has, 

 even at the present day, any generally recog- 

 nized position • among biologists themselves. 

 That this has been the case for many years, 

 even in Europe, is evident from the fact that 

 until recently the published results of investi- 

 gation in the field of physiological chemistry 

 have had to be sought for in widely diverse 

 places. Many papers have been published in 

 purely chemical journals, others in journals 

 devoted to physiology, while still others have 

 appeared in so-called ' natural-history ' jour- 

 nals, — a fact which in itself plainly indicates, 

 the past status of this branch of science. 



There can be no question that physiological 

 chemistiy should occup} T a definite place among 

 the biological sciences. Biology is confessedly 

 a study of life, and, as such, has to do with the 

 development, structure, and function of living 

 organisms. The first two of these we suppose 

 to be included under the heads of embiTology 

 and morphology ; while the third, constituting, 

 in the words of Herbert Spencer, " the second 

 main division of biology, embracing the func- 

 tional phenomena of organisms, is that which 

 is in part signified by physiology." Further, 

 '•that part of physiology which is concerned 

 with the molecular changes going on in organ- 

 isms is known as organic chemistry," or, with 

 equal propriety, as physiological chemistry : 

 hence a stud}' of the functions of the body, 

 to be at all complete, must include a study 

 of the chemical changes incident to life, and 

 cannot be restricted to the purely physical 

 phenomena of the organism. Yet it is ver}- 

 noticeable that wherever ' biology ' is taught in 

 this countiy, even in the most liberall} T con- 

 ducted institutions, where the course of study 

 embraces embryology, animal and vegetable 

 morpholog3 T , experimental pbysiologj*, etc., 

 physiological chemistry is rarely mentioned.^ 



We need to inquire whether this is due to a 



