812 



SCIENCE. 



[N. S. Vol. XXI. Ko. 543. 



that this is not the case. The deflection 

 decreases with increase in depth up to a 

 certain point and beyond that it increases. 

 The computations of Professor Merriman 

 indicate that the depth of truss which gives 

 the least deflection or the greatest stiffness 

 is a little less than the economic depth. 

 He also showed that the relation between 

 the economic depth and the span of the 

 bridge applies very closely to the depth 

 which gives the greatest stiffness. 



On the Dispersion, Absorption, Fluores- 

 cence and Magnetic Rotation of Sodium 

 Vapor: Professor Robert Williams 

 Wood, of Baltimore. 



A Photographic Study of the Diffusion of 

 Ultra-Violet Light by Gas Particles: 

 Professor Robert Williams Wood, of 

 Baltimore. 



On the Use of the Falling Plate Oscillo- 

 graph as a Phasemeter: Dr. William 

 McClellan, of Philadelphia. 

 The three general methods for obtaining 

 the form of an alternating current wave 

 are— by means of contact-maker and meter, 

 by means of a curve-tracer and by means 

 of an oscillograph. With the first and sec- 

 ond methods the current must be kept ab- 

 solutely constant, as some time is necessary 

 to take the numerous readings required to 

 plot the curve. The oscillograph gives 

 a picture of a single wave. Essentially it 

 is a sensitive moving-coil mirror galvano- 

 meter, with a period of about one ten- 

 thousandth of a second. It is able, there- 

 fore, to follow easily currents of commer- 

 cial frequency. To obtain the wave form 

 it is necessary to have a uniform motion 

 perpendicular to the motion of the coil. 

 This is obtained by synchronous motors, 

 revolving films or a falling photographic 

 plate. The latter has been found to be 

 very convenient, though its motion is uni- 



formly accelerated instead of uniform. 

 The error is small, however. 



With a double oscillograph, that is one 

 that can draw two curves simultaneously, 

 for example the current and voltage waves 

 of a single circuit, we can immediately see 

 the possibility of a phasemeter. To test 

 the accuracy of the irustrument when used 

 in this way, an Ayrton and Perry stand- 

 ard of self-induction, of known resistance, 

 was used. Current and electromotive force 

 waves were obtained and the angle of lag 

 measured. These were compared with the 

 values calculated from the constants of the 

 standard. 



On the Brains of Scymnus, Mitsukurina 

 and Chlamydoselachus, with Remarks 

 upon Selachian Bi-ains from Standpoints 

 Morphic, Ontogenic, Taxonomic, Phylo- 

 genic and Pedagogic: Professor Burt G. 

 Wilder, of Ithaca. 



Of the three sharks named in the title 

 all occur in Japanese waters. Mitsukurina 

 (which may be called the 'rostrum shark' 

 from the extraordinary projection of the 

 snout separated from the upper jaw by a 

 deep notch) was first described in 1898 by 

 Jordan and has not, as yet, been found else- 

 where ; it is so remarkable, and the ex- 

 amples already obtained are so few that 

 the specimen exhibited cost about $75.00 

 So far as the speaker is aware its brain has 

 never before been studied. Chlamydose- 

 lachus is also very rare, but besides the 

 Japanese specimens at least one has been 

 taken oft' Madeira. It was described in 

 1884 by Garman, who suggested 'frilled 

 shark' as a popular name, referring to the 

 folded covers of the gill-slits, of which 

 there are six instead of five as with most 

 modern sharks. The body is so long and 

 snake-like that Garman gave it the specific 

 name anguineus, and perhaps a good pop- 

 ular title might be the English form, an- 

 guin ; it has even been thought by some that 



