200 



NATURE 



(July 2, 190^ 



leaves the mercurial surface, and generally bursts in 

 doing so. 



Considerable impurities in the mercury do not render the 

 production of these bubbles impossible. Very stable bubbles 

 may be formed of mercury contaminated with sodium. But 

 the most stable have been formed from mercury recently 

 cleaned with dilute nitric acid followed by a solution of 

 caustic potash. 



Another striking and beautiful experiment with the pro- 

 duction of these bubbles may be made by directing a strong 

 jet of water into a shallow vessel containing some mercury. 

 The stream of water, carrying air bubbles with it, pene- 

 trates the supernatant water and impinges on the mercury 

 below. There it forms numerous bubbles of various sizes 

 contained in mercury pellicles, many of which detach 

 themselves from the mercury below, and are carried about 

 in the water. The stability of these bubbles is amazing. 

 They are often whirled round and round in the turbulent 

 motion of the water for several seconds without bursting. 



Henry H. Dixon. 



Botanical Laboratory, Trinity College, Dublin. 



Radium Fluorescence. 



If a tube containing radium bromide is wrapped in black 

 paper and brought within three or four inches of the eye, in 

 a dark room, a curious sensation of general illumination 

 of the eye is experienced ; this occurs whether the eyelid is 

 closed or not. It is difficult accurately to describe the 

 sensation produced ; the eye seems filled with light. This 

 effect can readily be detected when six florins are placed 

 between the closed eye and the sample of radium. 



Probably the effect is due to general fluorescence of every 

 part of the eye, for fluorescence seems to be a commoner 

 property of matter than hitherto suspected. 



The following substances are distinctly fluorescent under 

 radium radiation : — 



Opal Glass. 



Soda Glass. 



Lead Glass. 



Uranium Glass. 



Didymium Glass. 



Celluloid. 



Mother of Pearl. 



Mica. 



Borax, 



Alum. 



I have been unable to detect decided fluorescence in the 

 following substances, however, with a more powerful source 

 of radiation, or a more sensitive receiver than the eye ; 

 possibly some of these might be placed in the first list : — 



Potass Bichrom. Selenium. 



Ruby Glass (flashed). Plaster of Paris. 



Prepared Chalk. lodosulphate of Quinine. 



Ebonite. Woods (various). 



Silk. ^ Camphor Monobromate. 



In the case of translucent substances, the effects are best 

 observed by looking through the substance, placing the 

 tube of radium nearly in contact with the far side. If the 

 experiments are carried on too near the eye, the direct 

 fluorescence of the eye itself interferes with accurate observ- 

 ations. 



Little cups made of thick tinfoil are very convenient for 

 the examination of liquids ; the open vessel is viewed from 

 above, the radium being placed below the cup. 



It is important to well prepare the eye by excluding every 

 trace of light from the room for at least a quarter of an 

 hour before the experiments are made. 



F. Harrison Glew. 



156 Clapham Road, S.W., June i. 



Yellow Resin. Liquid Paraffin. 



Cotton Wool. Turpentine. 



White Paper. Chloroform. 



Cupri Sulph. Water. 



Quinine Sulph. Glycerin. 



A New Series in the Magnesium Spectrum. 

 In your issue of April i6 there is an abstract of a paper 

 communicated by Prof. Fowler on the above subject to the 

 Royal Society. He shows that his new series is of the same 

 type as the special series for magnesium discovered by 

 Rydberg, and represents it by a similar formula to that 

 used by Rydberg. But in " The Cause of the Structure of 



NO. 1757, VOL. 68] 



Spectra " {Phil. Mag., September, 1901) I have shown that 

 the Rydberg series for magnesium can be represented by 

 a formula which brings out the existence of harmonics in 

 atomic vibrations. These can be demonstrated in the 

 hydrogen spectrum also, but it seemed to be of interest to 

 inquire whether the new series gives a further example of 

 the existence of optical harmonics. It does, for the vibra- 

 tion numbers of its four lines can be given by the formula 



« = 39730- _ JL°725?__ 



(2-9TJ-2-02llsf 



where s has the values 4, 5, 6 and 7. 

 This may be written approximately as 

 107250 



39730- 



{3-o-023-(2 + o-023)/4-^ 

 while Rydberg 's special series is represented by 

 ^ = 39730- ^°725 ^ 



I have not thought it worth while to test whether the 

 harmonic formula for the new series is as successful as 

 Rydberg's in giving the wave-lengths accurately, as the 

 evidence for the existence of optical harmonics is what I 

 wish to draw attention to. In Rydberg's series 5 has all 

 the integral values from 3 to 8. In the new series Prof. 

 Fowler gives wave-lengths for which s has integral values 

 from 4 to 7. We might expect the lines for 5=3 and s = 8 

 to be yet found. Their wave-lengths by the harmonic 

 formula would be 5125-8 and 3956-3. 



Melbourne, May 27. William Sutherland. 



the kite competition of the 

 aeronj\utical society. 



THE kite competition for the silver medal of the 

 Aeronautical Society of Great Britain took place 

 on Thursday, June 25, on the Sussex Downs, at 

 Findon, near Worthing, by permission of Lord Henry 

 Thynne. The conditions specified that a weight of 

 two pounds as representing the weight of recording 

 meteorological instruments should be carried, and that 

 the medal should be given for the highest flight at- 

 tained by a single kite above 3000 feet. The altitude 

 of the kites was to be determined by trigonometrical 

 observations. 



The locality proved to be admirably adapted for the 

 competition under the conditions of weather prevailing 

 at the time. A light wind from the south-west blew 

 up the slope of the Downs in the morning, and in- 

 creased to a steady breeze in the afternoon, backing 

 sornewhat to the southward as the day, which was 

 beautifully fine, went on. 



It was understood that observations of the altitude 

 of the kites should be commenced after the lapse of 

 an hour from the signal for starting. By 2.45 p.m. 

 stations for the kite reels had been arranged, 200 yards 

 apart, along the slope of the Downs, and two stations 

 for the theodolites, 700 yards apart, were selected, 

 from which the kite stations were visible, and which 

 were likely to command an uninterrupted view of the 

 kites during the flight. The responsible duty of 

 carrying out the measurements with the theodolites 

 and the auxiliary chaining was most kindly under- 

 taken by Mr. J. E. Dallas and Mr. W. F. Mackenzie, 

 of the Royal Indian Engineering College, Coopers 

 Hill, and the success of the arrangements was due 

 in no small degree to the assistance afforded by these 

 gentlemen. 



At 2.45 the signal was given to start, and at 3.45 

 observations of height commenced. The synchronism 

 of the observations of any particular kite from the 

 two stations was secured at first by a prearranged 

 code of signals from one theodolite station to the 

 other, and subsequently by telephone between the two 

 stations. Eight kites were entered for the competi- 

 tion, but only six appeared on the ground, and only 



