Oct., TO04. 



KXCnVI.KPGE & SCIFNTIFIC NEWS. 



245 



has been substituted. The hehx of wire consisted of 5000 

 turns, the length being joo centimetres. If such a helix is 

 placed in connection with an oscillating circuit consisting of a 

 condenser or Leyden jar, a spark gap, and a variable induct- 

 ance, stationary waves can be set up on the helix by adjusting 

 the inductance in the oscillating circuit. In order to detect 

 the nodes and antinodes of these stationary oscillations. Pro- 

 fessor Fleming makes use of a vacuum tube, similar to that used 

 in spectrum analysis, and preferably one filled with the rare 

 gas. Neon. Rarefied Xeon seems to be extremely sensitive to 

 the presence of variable electric force through it ; hence, if 

 such a tube is held perpendicular to the helix, .and moved 

 parallel to itself along it, it glows brightly at the antinodes, but 

 not at the nodes. In this manner the internodal distances 

 can be measured with considerable accuracy, and the wave- 

 length of the stationary oscillation measured. 



Now the velocity with which the wave is propagated along 

 the spiral can be shown to be inversely proportional to the 

 square root of the product of the capacity and inductance of 

 the hehx per unit of length. Professor Fleming has perfected 

 of late years methods for measuring very small capacities and 

 inductances, and in the case of the above-named helix the in- 

 ductance is equal to 100,000 centimetres per centimetre, 

 whilst a capacity of the helix is ,"„ of a micro- microfarad. 

 (I micro-microfarad = lo^' microfarad.) 



From these data the velocity of propagation of electric 

 waves along the helix can bs shown to be 235.030.000 centi- 



along it can be calculated as above shown, and hence the fre- 

 quency of the oscillating circuit becomes known. If this 

 freciuency is divided into the velocity of light, reckoned in 

 feet, it gives the wave-length in feet of the wave radiated from 

 the associated aerial, provided that the aerial radiating wire 

 has been tuned to be in resonance with this oscillating 

 circuit. 



This instrument also pnivides tin- means of measuring sm.all 

 inductances, and also the frequencies in oscillating circuits, 

 which are much higher th.ui those wliich can be determined 

 by photographing the spark. 



Thought R^a-ys. 



M. di BvAzzh, a student at Liege, who sent an account of 

 Becquerel's work on radio-activity to the Scculo A'.V. for 

 January, 1903, now describes the I-r,ays as discovered by 

 himself when repeating the N-ray experiments of M. Blondlot 

 and of Professor Charpentier. Charpcntier succeeded in 

 demonstrating that the human body emits Nrays. He found 

 that the phosphorescence of certain substances is increased 

 when they are brought close to a nerve or contracting muscle, 

 i.t\ muscular work is accompanied by a marked emission of 

 N-rays. By means of a simple apparatus, a lead tube 7 cm. 

 long (lead was chosen because it was opaque to the human 



Professor Fleming's Kummeter. 



metres per second. This figure is confirmed in the following 

 manner: The capacity and the inductance in the oscillating 

 circuit are both measured when the first harmonic oscillation 

 is formed on the helix, and under those conditions the h.alf 

 wave-length was found to be 140 centimetres, whilst the 

 frequency in the oscillating circuit, as calculated from the 

 capacity and inductance, was found to be o'iS47 x lo". 



Having, therefore, the wave-length and frequency, we find 

 their product gives a velocity of 235,000,000 centimetres per 

 second, which agrees with the figure determined from the con- 

 stants of the helix. 



The best form of inductance to be employed in connection 

 with the oscillating circuit is a square of one turn of wire; the 

 employment of spiral coils leads to errors due to passage of 

 a dielectric current from coil to coil. The improved instru- 

 ment which Professor P'leming has now constructed, and 

 which is based on the foregoing considerations, he calls a 

 "Kummeter." It is constructed as follows: A long ebonite 

 rod is wound over closely with silk-covered wire in one layer, 

 and this is supported on insulating stands. On this long helix 

 slides a metal saddle having some layers of tinfoil interposed 

 to make good contact between the saddle and the helix. This 

 saddle is connected by a flexible wire with the earth. One 

 end of the helix is furnished with an insulated metal plate, 

 which is placed in apposition to another metal plate connected 

 to the oscillating circuit of the transmitter. The process of 

 measuring the wave consists in sliding the saddle along until 

 a Neon vacuum tube indicates the presence of one node half- 

 way between the saddle and the plate. When this is the case 

 the distance from saddle to plate is one wave-length of the 

 stationary wave on the helix. 



From the constants of the helix the velocity of the wave 



rays, and accordingly lessens diffusion), closed at the end by 

 a sheet of paper, or bit of silk covered with phosphorescent 

 calcium sulphate, it is possible to observe the different nervous 

 centres of the cerebral cortex. Thus by placing it in appo- 

 sition with Broca's centre (the centre of articulate speech) 

 while the patient is talking, variations are produced in the 

 luminosity of the phosphorescent calcium sulphate. In 

 another experiment, Charpentier saw the phosphorescent 

 substance shine all down the line of its application to the 

 spinal cord. Charpentier concluded that the emission of rays 

 goes pari passu with activity of function, whence we should be 

 in possession of a new method of stuilytng nervous and mus- 

 cular activity. Di Brazzil claims to liave demonstrated what 

 Charpentier only surmised, i.e. that " the brain is the seat of 

 active radiation." The I (Italy) rays differ from the N in 

 that they can pass through moist substances, and are not bent 

 nor refracted. Di Brazzi observes them directly and indirectly. 

 In direct observation he applies a phosphorescing screen 

 treated wiih platinocyanide of Ba.,or other phosphorescent 

 substances, to the patient's head. The screen is faintly illumi- 

 nated by a radiographic tube (tubo-focus) enclosed in a 

 wooden box. When the subject concentrates his will, curious 

 oscillations appear in the luminosity of the screen in relation 

 with the patient's psychical activity. When his attention is 

 not concentrated, the light does not flicker. The rays are not 

 emitted equally from all parts of the head. They are nil at 

 the forehead and upper part of Broci's centre, increase at 

 the temples and eyes, and reach their maximum behind the 

 ears. In photography, precautions must be taken to secure 

 uniform length of exposure (di Brazza introduces an automatic 

 interrupter), sensitivity of plate, conditions of development, 

 6cc. Di Brazza always uses ortho chromatic plates. 



