*34 



NA TV RE 



\June 8, 1882 



Our great countryman, Mr. Wallace, who, we believe, 

 met with this ground-cuckoo in Sarawak, also speaks of 

 its terrestrial habits, and states that its mode of life 

 resembles that of the pheasants of the genus Euplocamus. 

 Little else appears to have been recorded respecting this 

 cuckoo, which is certainly one of the most peculiar forms 

 of bird-life that have of late years been exhibited in the 

 Zoological Society's aviaries. 



On examining the specimen in question, which, when 

 it first arrived, had only a half-grown tail, but is now in 

 excellent plumage, it will be at once observed that the 

 naked space round the eye has been incorrectly coloured 

 in Temminck's figure of this species. Instead of being 

 of a red colour as there represented, it is of a nearly uni- 

 form pale green, as is likewise the bill. Few non-pro- 

 fessional ornithologists, indeed, would recognise a cuckoo 

 in the pheasant-like ground-loving bird with large bright 

 bill, which is labelled in the Zoological Societj's Gardens 

 " The Radiated Ground-Cuckoo." 



MR. STROH' S VIBRATORY EXPERIMENTS 

 A CENTRE of attraction at the recent Paris Electrical 

 •**■ Exhibition was the Norwegian section, in which 

 Prof. Bjerknes of Christiania exhibited his remarkable 

 experiments with little drums or tambours vibrating under 

 water, and attracting or repelling each other according as 

 the phase of the pulsations was like or unlike. An 

 account of his results was published in Nature, vol. xxiv. 

 p. 361, and the analogy between them and the well-known 

 effects of magnetism was there drawn attention to. The 

 field opened up by Prof. Bjerknes has been entered 

 by Mr. Augustus Stroh, a well-known member of 

 the Society of Telegraph Engineers and of Electri- 

 cians, who recently delivered a lecture on his re- 

 searches. Mr. Stroh has gone over the experiments 

 of Dr. Bjerknes in air as a medium for propagating the 

 pulsations of the drums instead of water, and has ad- 

 vanced beyond his predecessor in further experiments on 

 the same line. The beauty of the apparatus and methods 

 devised by him, and the exquisite skill with which he 

 manipulated them, elicited the unanimous admiration of 

 his hearers. 



The drums employed by Mr. Stroh were small shells 

 of wood having their mouths covered by an elastic mem- 

 brane and their rears communicating with a flexible pipe, 

 through which the pulsating air was communicated to the 

 membrane, so that it could cause the latter to bulge out 

 -or collapse at every wave of air. The source of the 

 vibrations was a vibrating reed, against which the air 

 was forced by a small hand-bellows shaped like an 

 accordion. By employing a flexible forked tube with 

 arms of equal length, each fitted with a drum at the end, 

 the vibratory air-blast from the reed could be conveyed 

 to the drums so as to set them vibrating in like phase ; 

 and when one of the drums was mounted on a vertical 

 axis, and free to rotate round it like the pole of a balanced 

 magnetic needle, the approach of the other drum to it 

 resulted in an attraction between them which was verv 

 pronounced. In this case the drums were vibrating in 

 like phase, that is to say, they both bulged out and bulged 

 in simultaneously. The mechanical explanation of the 

 attraction is that there is a rarefaction of the air between 

 the drums produced by the simultaneous advance and 

 recession of the membranes toward each other. This 

 rarefaction occasions a difference of pressure between 

 the front and backs of the drums, causing them to move 

 towards each other. 



When, however, the vibrations are in opposite phase, 

 that is to say, when one drum bulges out while the other 

 bulges in, there is a repulsion between the drums corre- 

 sponding to a condensation of air in the space between 

 them. This condition of things is ingeniously obtained 

 by means of an electromagnetic air-pump or bellows 



devised by Mr. Stroh. It consists of an iron armature 

 placed between the poles of two double electromagnets, 

 and free to move alternately towards either electromagnet. 

 This to-and-fro motion of the armature is kept up by 

 making and breaking the battery circuit in the coils of 

 the electromagnets alternately. The armature carries a 

 cross-arm or lever-rod fixed at right angles to its axis, 

 and the ends of the rod are attached to two leather dia- 

 phragms, which act as partitions across the interior of 

 two boxes. Each of these two boxes communicates with 

 the external air by two pipes or orifices, one on each side 

 of the leather partition. Now when this diaphragm or 

 partition stretching across the box oscillates, air is ex- 

 pelled from one compartment of the box, and at the same 

 time air rushes into the other through the orifices pro- 

 vided. It follows that if the orifices communicate with 

 two drums one drum will collapse whilst the other is 

 inflated. Now the oscillations of the armature keep the 

 diaphragm oscillating, and hence the two drums commu- 

 nicating with opposite compartments of the air-chamber 

 are kept vibrating in unlike phase. By employing two 

 such air-boxes or pumps Mr. Stroh is able at a moment's 

 notice to change the vibrations of the two drums from 

 like to opposite phase by simply connecting the drums to 

 the two expelling compartments of the two boxes, or one 

 to an expelling and the other to an indrawing compart- 

 ment of the box. The same device of a pivoted drum 

 served in this case also to show that when the drums 

 were vibrating in unlike phase there was repulsion between 

 them. 



In the science of magnetism we are taught that like 

 poles repel and unlike poles attract ; but in the experi- 

 ments we are considering it is the drums in like phase 

 which attract and those in unlike phase which repel. Mr. 

 Stroh does not attempt to theorise upon his results; but 

 if the analogy with magnetism hold good our ideas of 

 what constitute like poles in a magnet will suffer a con- 

 siderable change. 



The aerial analogy for the attraction which always takes 

 place between a piece of soft iron and a magnetic pole, 

 whether it be a north or a south pole, was illustrated by 

 Mr. Stroh in holding quiescent or non- vibrating bodies, 

 such as his hand, or a piece of cardboard, near to either 

 drum. The result was always an attraction of the drum 

 towards the passive surface presented, whatever the phase 

 of the drum. This attraction was prettily shown by 

 means of a small round disk of paper attached to the 

 end of a delicate lever pivoted on an upright stand like a 

 magnetic needle. 



The dying oscillations of the pole of a magnetic needle, 

 when brought to rest in front of a disturbing magnet, 

 were further illustrated by Mr. Stroh, in presenting the 

 free drum a little apart from the pivoted one, and ob- 

 serving the latter shift round and oscillate before the 

 other, until it came to rest face to face with it. This of 

 course happened when the two drums were vibrating in 

 like phase. When they vibrated in opposite phase, the 

 pivoted drum moved away from the free one, and came 

 to rest further off. 



Until this point Mr. Stroh had been occupied with 

 repeating Dr. Bjerknes' experiments in air; but beyond 

 this he makes a new departure on his own account. The 

 object of his further experiments was to ascertain what 

 goes on in the air between the vibrating drums ; and by 

 inclosing a pair of the drums in an air chamber com- 

 municating wiih a capillary tube containing a column of 

 spirits of wine to act on a pressure guage he showed that 

 when the vibrations were of like phase, the spirit fell, 

 indicating that the air was expelled from between the 

 drums, and on the contrary, when the vibrations were of 

 unlike phase, the spirit rose in the tube, indicating that 

 air had been drawn into the space between the drums, 

 and the pressure thereby raised. 



The most valuable part of Mr. Stroh' s results was now 



