June, 1904 



KNOWLEDGE & SCIENTIFIC NEWS. Vs^l-d^-^) i 



31 



it can be shown that these birds can be farmed at a profit, 

 as in the case of the Ostrich. So far, however, all en- 

 deavours to start a new industry of this kind appear to 

 have ended in failure. 



It is to be hoped that even imitation " Ospreys " will 

 be eschewed in future, until some substitute for real 

 feathers can be found which will possess the airy •,'race 

 of the genuine " Osprey," or until they are made of 

 feathers taken from birds bred for this purpose, or from 

 some domesticated species. As it is, the good resolution 



Hig. 4. -An "imitation o>prey" as sold in milliner's .shop; said to be 

 made of vultures feather's. It is really made by splitting and 

 twisting feathers of the Rhea, or South American Ostrich. 



to wear only imitation "Ospreys" would create as much 

 mischief as the wearing of the genuine plume, since the 

 species called upon to furnish the " imitation " would 

 themselves sooner or later suffer extermination. 



Finally, "Imitation Ospreys" are simply made by 

 using the feathers of other birds, and up to the present 

 time these have been of wild birds. The statements 

 that imitation or artificial Ospreys are made of split 

 quills, whalebone, or other material, are all absolutely 

 false. 



Electric 

 Wave MeaLSvirement. 



Dr. J. A. Fleming, F.R.S., exhibited at the Royal 

 Society Soiree a very ingenious and interesting device 

 for the measurement of electric wave lengths. The 

 principle of the method will be grasped by anyone who 

 has watched sea waves impinging against and rebound- 

 ing from a sea wall. The returning waves sometimes 

 reinforce and sometimes neutralise the oncoming ones, 

 so that here we have a wave crest raised above its 

 fellows, and there a wave neutralised or eliminated. If 

 the waves were all quite regular, and were uniformly 

 propelled and reflected, these points of reinforced and 

 eliminated waves would be fixed. We should in short 

 have "nodes" and "loops" of force in the train of 

 waves. Dr. Fleming's apparatus for showing the nodes 

 and loops of an electric train of waves consisted of a 



spiral of fine wire, along which the discharge of two 

 Leyden jars propelled vibrations varying in number 

 between a quarter of a million a second. The re- 

 sultant electric wave travelled along the spiral at about 

 fifteen hundred miles a second, was reflected and 

 returned, thus establishing on the wire stationary electric 

 waves, just as stationary aerial waves are produced in an 

 organ pipe. The position of the nodes and loops was 

 ascertained by use of a series of carbonic dioxide vacuum 



<rr. 



A, B.— Lonji coil of 5,000 turns of 



No. .((> wire. 

 W. liurth wire. 

 Li, Lj.— l-eyden Jars, each '0014 



mfd. capacil>. 

 X. Variable Inductance Coil, o-2.;o 



microhenry's. 

 I. Induction Coil — lo-inch spark. 

 S. — Spark balls. 



lubes, which glowed when near a loop — the point where 

 the oncoming and returning waves joined to produce a 

 region of maximum electric force. Some further details 

 of the apparatus are as follows : — 



The long solenoid of silk covered wire has 5000 turns 

 and a total length of 643 metres. This solenoid has 

 parallel to it an adjustable earth wire and a divided scale. 

 The solenoid is connected to one point on an oscillatory 

 electric circuit consisting of a couple of Leydens having 

 a capacity of 0-00068 mid. and an adjustable inductance 

 of o to 230 microhenrys and a silent discharger. When 

 oscillations are set up in this circuit by induction coil 

 discharges, and the fretjuency adjusted, stationary electric 

 waves are set up in the solenoid. 



The position of the first node is always well defined. 

 Theory indicates that the distance from the end of the 

 solenoid to the first node should be to the distance 

 between the first and second nodes in the ratio of 1:2-5, 

 and that the distance between the first and second nodes 

 should be half a wave length. Experiments with this 

 apparatus give a mean value of i : 2-4 for the above ratio 

 for the first five odd harmonics. 



The inductance of the long spiral is 100 microhenrys 

 per centimetre of length and its capacity is 26 x 10"" of a 

 microfarad per centimetre of length. From these data 

 the velocity of the wave along the spiral is found to be 

 about 196 million centimetres per second.'' From the 

 wave lengths experimentally determined the correspond- 

 ing frequencies are then found, and these agree substan- 

 tially with the frequencies as calculated from the induct- 

 ance and capacity of the Leyden jar circuit that is 

 employed. Thus, corresponding to the first odd har- 

 monic the node is 64 centimetres from the end. The in- 

 ductance in the jar circuit is then 79 microhenrys, and 

 the frequency as determined from the node -position and 

 wave-velocity is 720,000 complete oscillations per second ; 

 whilst from the jar circuit inductance and capacity it is 

 690,000, or in fair agreement. The practical interest of 

 the apparatus lies in the fact that it is in actual use for 

 measuring the lengths of wireless electric waves such as 

 are sent out from the station at Poldhu, in Cornwall. 



5 X I06 



4 /Capacity of Jar in 

 » microfarads 



Frequency 



See Dr. Fleming's Cantor Lectures, 1900 



Induction of Coil 

 in c.m.s. 



