May 14, 1891] 



NATURE 



31 



Mr. Forbes exactly gives the difference, as thinner, more 

 wiry, and high pitched ; it is also shorter, at least in the wild 

 G. ferrngina. These I have often heard crowing, and shot in 

 the extreme east of Asam, where for a very large area, on the 

 Upper Diking River, and across Patkai, there are no inhabitants. 



This same G. ferriigina is, however, to be found wild all 

 over Asam, and the countries around ; eggs found in the jungles 

 are often hatched under domestic fowls, and hence these are 

 frequently crossed, and the crow of the cock varies much in 

 consequence. 



But the difference between the wild G. ferrttgina and our 

 "barn-door" cock, in this particular, is so well marked that it 

 could invariably be detected. 



I may perhaps mention a curious sight I saw last year, within 

 ICX3 yards of my bungalow, in the evening. A cloud of white 

 ants were rising on the air, in the main road, and a jackal and 

 jungle cock were busy eating the "neuters" swarming all over 

 the ground ; presently another jackal joined and the cock was 

 between them : all were so busy feeding that they took no notice 

 of each other, the jackals often lying on their bellies, while the 

 cock moved about between them, at 2 or 3 yards only. By this 

 time 15 or 20 people were looking on and laughing. Suddenly 

 a third, younger jackal, joined the group, and after eating the 

 ants a short time, and walking about like the others, dropped 

 into the ditch and stalked the cock, crouching close to him. 

 The latter at once flew, and made a bee line for the forest 400 

 yards off. The total area of the ants was about 20 feet by 8 

 only. S. E. Peal. 



Sibsagar, Asam, March 27. 



Antipathy [?] of Birds for Colour. 



With regard to the destruction of the yellow crocus by the 

 sparrow, mentioned by your correspondent " M. H. M." in 

 Nature, vol. xliii. p. 558, this bird appears to have a pre- 

 dilection for yellow. In an article on "Birds' Nests and Nest- 

 building," in the Animal World, present number, an instance 

 is given of sparrows using the flowers of the laburnum for 

 their nest. Only lately I have been watching^ them picking out 

 the yellow centres of the daisy, but in this case it was for food, 

 and I am inclined to believe that some portion of the crocus is 

 also eaten. At this time of the year they are well known to be 

 partial to buds and flowers of different kinds — for instance, the 

 blossoms of the gooseberry bushes. 



Doubtless, the bright yellow colour attracts the attention of this 

 now much censured bird, so omnivorous in his tastes and such a 

 general scavenger, and therefore not wholly to be condemned. 



Clevedon, April 28. T. B. J. 



The Destruction of Fish by Frost. 



Referring to Prof. Bonney's letter in Nature, vol. xliii. 

 p. 295, regarding the destruction of fish by frost, and in which 

 he asks for information from more northern latitudes, I may say 

 that during the winter of 1885-86, at Cape Prince of Wales, 

 Hudson's Strait, when the thickness of ice in a small lake was 

 being measured, live fish were often seen ; and upon the last 

 occasion, when the ice measured six feet and half an inch, several 

 were thrown up with the water that, upon our cutting through, im- 

 mediately overflowed. These fish were about an inch and a half 

 in length and were extremely lively. I may add that during the 

 summer both feeder and outlet of the lake averaged about eight 

 inches in depth and the lake nine feet in its deepest part. The 

 former ceased to flow on November 8, when, too, ice, fourteen 

 inches in thickness, covered the lake. F. F. Payne. 



Meteorological Service of Canada, 

 Toronto, April 16. 



The Flying to Pieces of a Whirling Ring. 



With reference to the recent discussion in your columns on 

 the whirling of steel bands, the following results will be of 

 interest. 



A weldless steel flask, with spherical body 12 inches in 

 diameter and g inch thick, constructed for use in a centrifugal 

 milk separator, to revolve about its axis of symmetry at a normal 

 speed of 7000 revolutions per minute, was whirled at a gradually 

 increasing speed, with a view to ascertaining the "bursting" 

 velocity. 



At 16,000 revolutions per minute the body of the flask had 



NO. I I 24, VOL. 44] 



bulged 2 inches in diameter : this is equivalent to an extension 

 of 17 per cent, of the circumference ; the peripheral speed being 

 840 feet per second, and the tension 31 '5 tons per square inch. 



The experiment was not continued, as it was considered suffi- 

 ciently satisfactory, and the bulged flask is kept as a curiosity. 

 Chas. a. Carus-Wilson. 



McGill University, Montreal. 



HERTZ'S EXPERIMENTS} 

 III. 



IN the last article the principles upon which a rapidly 

 vibrating electric oscillator should be constructed 

 were considered, and how the sudden break-down of the 

 air gap enabled these rapid vibrations to be started. It 

 is probable that this break-down occurs in a time 

 smaller than the thousand millionth of a second. How 

 very rapid interatomic motions must be ! 



Consider now the principles on which an apparatus is 

 to be constructed to receive the vibrations produced by 

 this oscillator. We may observe in the first place that 

 as we are dealing with a succession of impulses at equal 

 intervals of time we can utilize resonance to accumulate 

 the effect of a single impulse. Resonance is used in 

 an immense variety of circumstances to accumulate the 

 efifect of a series of impulses, and is avoided in another 

 immense variety of circumstances to prevent accumulating 

 the effect of a series of impulses. We see, we hear, we 

 photograph by using it ; we use .it to make musical 

 sounds, to keep clocks and watches going, to work tele- 

 graphs. By avoiding it carriages drive safely over rough 

 roads, ships navigate the seas, the tides do not now over- 

 whelm the land, the earth and planets preserve their 

 courses round the sun, and the solar system is saved 

 from destruction. Resonance may be thus described : — 

 If a system is able to vibrate by itself in any way, and if 

 we give it a series of impulses, each tending to increase 

 the vibration, the effect will be cumulative, and the vibra- 

 tion will increase. To do this the impulses must be well 

 timed, at intervals the same as the period of vibration of 

 the system itself. Otherwise some of the impulses will 

 tend to stop the vibration, and only some to increase it, 

 and on the whole the effect will be small. In order to 

 use resonance in the construction of the detector of waves 

 of electric force, we must make our detector so as to be 

 capable of an electric vibration of the same period as the 

 generator of the waves. If we do this we may expect the 

 currents produced in it to be increased by each wave, and 

 thus the electrification at its ends to increase, and so in- 

 crease the chance of our being able to produce a visible 

 spark. Two ways of using a detector have been men- 

 tioned. One is to observe the heating of a conductor 

 by the current in it, and the other to observe a spark due 

 to the electrification at the end of the conductor. The 

 latter is the most sensitive and has been most frequently 

 employed, and is the method first employed by Hertz. 

 Two forms of detector may be used for observing sparks. 

 One form consists of a single conductor bent into a circle 

 with its two extremities very close together. An electric 

 charge can oscillate from one end of this to the other round 

 the circle and back again. If the circle be the proper 

 size, about 70 cm. in diameter for the large sized oscillator 

 and about 8 cm. in diameter for the smaller sized one 

 described in the last article, the period of oscillation of 

 this charge will be the same as that of the charge on the 

 generator of the waves, and its oscillation will be increased 

 by resonance until, if the ends of the circular wire be close 

 enough together, the opposite electrification of the ends 

 will become great enough to cause a spark across the 

 gap. The other form of detector depends on using tv/o 

 conductors, each of which has the same period of electric 

 oscillation as the oscillations we wish to detect. These 



' Continued from p. 14. 



