252 



NA TV RE 



[July 13, 1893 



Research Bay, Spilzbergen, the gigantic front of the two glaciers 

 which flow into the sea presented three different tints. At the 

 base some parts were quite dark, suggesting deep caves, but 

 really consi-ting of pure homogeneous, compact ice. The middle 

 region was greenish-blue, and the upper, consisting of snow- 

 ice, was white. The ice-floes were either white or greenish- 

 blue, or of an extremely intense emerald green. Ontatingone 

 of the latter out of the water it was found to consist of homo- 

 geneous limpid ice, absolutely colourless to the thickness of I m. 

 or so. The deep green colour was due to its illumination by 

 the green water of the b\y, which, like that of the Isfjord, is of 

 an intensely green colour. 



An important paper by Messrs. Sarasin an 1 De la Rive is 

 published in \'a^ Archives des Sciences Physique et Na.turelles and 

 -ontainsan account of a series of experiments on the interference 

 of electrical waves after reflection from a metallic screen. The 

 authors being of opinion that the results obtained by lier'z and 

 themselves in a former investigation were vitiated on account of 

 the reflecting surface being too small, undertook this series of 

 experiments, using as a reflecting surface a sheet of zinc l6 

 metres long and 8 metres high. The arrangement employed 

 was almost the same as that used by Hertz, the spark gap of the 

 oscillator, however, being surrounded by oil. The resonators 

 were circular, and had been used in a previous series of experi. 

 ments on the propagation of electrical waves along conducting 

 wires, in which it had been found that each resonator re- 

 sponds to waves of a definite wave-length, and to these only. A 

 series of observations, made with a view of ascertaining the 

 minimum size of mirror, which gives consistent results with 

 resonators of different sizes, showed that for a resomtor of 75 cm. 

 in diameter the reflecting surface must have a length of from 

 12 m. to 14 m. and a height of 8 m., while for a resonator of 

 35 cm. in diameter a mirror 5 m. long and 3 m. high is suflTicient. 

 The results obtained may be summed up as follows: — (l) A 

 circular resonator has a constant wave-length to which it 

 responds, whatever be the dimensions of the oscillator, the 

 strength of the induced spark only varies, attaining a maximum 

 value for a certain length of the oscillitor, which gives waves in 

 unison with the resonator. (2) The quarter wave length of a 

 circular resonator is approximately equal to twice its diameter. 

 (3) In the case of normal reflection from a metallic mirror the 

 first node coincides exactly with the surface of the mirror. (4) 

 The velocity of propagation of the electrical waves is the same 

 in air as along conducting wires. 



We have received a copy of a calibration curve of one of Prof. 

 Perry's new electric current meters, which are now being con- 

 structed for practical work by Messrs. Johnson and Phillips. 

 This meter, as some of our readers may know, consists of a 

 copper bell (with open neck) which rotates about its axis in a 

 radial magnetic field formed between an inner cylinder and an 

 outer surrounding cylinder, both of iron, and magnetised by a 

 coil surrounding the inner. As the surfaces of these cylinders 

 are furnished with teeth projecting towards one another, leaving 

 just sufficient clearance space for the ball, there are, alternating 

 with one another round the bell, places of maximum and mini- 

 mum field intensity. The bell is immersed in mercury, and 

 being covered with varnish, except at the lip and at the neck, 

 where it receives and gives oat current, is the seat of a current 

 sheet running from the lip to the neck. Thus the bell rotates 

 abDut its axis with a speed depending on the current flowing 

 and the intensity of the magnetic fiild. By the ingenious de- 

 vice of ren lering the field non uniform, the resisting couple due 

 to solid and fluid friction is made small in comparison with that 

 due to Foucault currents; and as the latter is proportional to 

 the square of the maximum field intensity multiplied by the 

 speed of ro'.atioa, and the driving couple to the product of the 



NO 1 237. VOT.. 48] 



field intensity and the current, a working formula is obtained in 

 which the current is proportional to speed and to field intensity. 

 By making the field sufficiently intense, the speed can be made 

 as slow as may be desired, and error from neglect of friction 

 proportionately diminished. The meter is thus very simple, 

 and unlikely to get out of order, or to be inconstant or untrust- 

 worthy in action. It is claimed, further, that the temperature 

 errors balance one another, and this is borne out by the fact 

 that the calibration curve is a straight line from the first current 

 marked, 25 amperes, to the highest, 60 amperes. The instru- 

 ment must therefore, within the range of currents for which it 

 is designed, work with great accuracy. 



The Philosophical Magazine for July contains a note by 

 Messrs. Harvey and Hird on some differences they have 

 observed in the behaviour of positive and negative electricity in 

 high frequency discharges. They find that, when a brush dis- 

 charge takes place in air between a point and a plate, the plate is 

 always positively charged, although the discharge is oscillatory. 

 In the case of hydrogen, however, the plate becomes negatively 

 electrified. Thus in the case of a brush discharge in air or 

 oxygen the positive electricity passes more readily than negative 

 from a point into any neighbouring conductor, while in 

 hydrogen the reverse takes place, negative electricity passing 

 more readily. 



Weber showed some years ago that the eggs of the common 

 pik^ could be caused to produce double monstrosities if the 

 recently fertilised ova were violently shaken. Mr. John A. 

 Ryder has recently ccm nnnicated a paper to the Aca- 

 demy of Natural Sciences of Philadelphia, which leads to the 

 belief that the Japanese produced their singular breeds of 

 double-tailed goldfishes by taking the eggs of the normal species 

 of goldfishes and shaking them, or disturbing them in some way, 

 as Prof. Weber did with the eggs of the pike. They would thus 

 obtain some complete double monsters, some with two heads 

 and a single tail, and some with double tails. Those most likely 

 to survive would be those with only a duplication of the tail. 

 These being selec'.ed and bred would probably hand down the 

 tendency to reproduce the double tail, a tendency which could 

 become fixed and characteristic if judicious selection were main- 

 tained. Mr. Ryder thinks that his investigation warrants the 

 conclusion that the regenerative power of organisms disappears 

 as we rise in the scale of organisation, last of all in the peri- 

 pheral extremital parts. He further observes that the power to 

 produce monstrosities or cogenital aberrations of development 

 due to external disturbances of segmentation, during growth, 

 diminishes in the higher forms /J/-/ passu with the advance in 

 development. 



In a number of papers communicated to the American 

 Philosophical Society, the American Academy of Arts and 

 Sciences, and the Boston Society of Natural History, Mr. A. S. 

 Packard gives the results of studies on the life-history of some 

 Bombycine moths. He has worked out the transformations of 

 several of the lower Bombyces, and has arrived at some valuable 

 results. He has treated the larvae as though they were 

 adult, independent animals, and has worked out their specific 

 and generic as well as family characters. The origin of mimetic 

 and protective characters has been traced, and the time of 

 larval life when they are assumed ascertained. This involves 

 a study of the development of the more specialised setae, spines, 

 tubercles, lines, spots, and other markings. Facts have also 

 been obtained withiegaid to the ontogeny of American species 

 and genera, which, when compared with the life-histories of 

 European, Asiatic, and South American Bombyces, may lead 

 to a partial comprehension of the phylogeny of the higher 

 Lepidoptera. 



