132 



NATURE 



[April 12, 191 7 



with Tripoli, June is q-2° warmer and December 

 2-6° colder. In the f>eriod under notice measurable 

 rain fell on only five days, to the amount of 20 mm., 

 and on fifteen others a few drops fell. The maximum 

 fall noted was 8 mm. on February 14, 1914, with 

 a N.W. wind. The cases of precipitation noted 

 occurred principally with winds from the north-west 

 and soutli-east. \\'inds are fairly evenly distributed 

 round the compass, there being no marked excess 

 from any one direction. In the year there were 251 

 cloudless and only twelve overcast days, the latter 

 confined to the months November to March. 



The theory of the immobility of the ether is ad- 

 vanced by Prof. P Zeeman in a short article in 

 Scientia for February (pp. 122-29). I" addition to 

 referring^ to the experiments of Fizeau and of Michel- 

 son and Morley, the author mentions a recent re- 

 determination which he undertook in 1916, using 

 monochromatic light. The results fully confirm Fres- 

 nel's formula, as completed with Lorentz's term, and 

 the hvpothesis of an immobile ether is in entire 

 accord with the observed effects. 



In contributing a paper on " Impact in Three 

 Dimensions " to the Proceedings of the Royal Irish 

 Academy (xxxiii., Section A, No. 6), Prof. M. W. J. 

 Fry has developed a subject on which a great deal evi- 

 dently remained to be said over and above what is con- 

 tained in Routh's "Rigid Dynamics." Some of the 

 results are almost at variance with preconceived ideas 

 on the subject. For example, while the velocity of com- 

 pression can only vanish once in the two-dimensional 

 problem, it may vanish three times in an impact in 

 three-dimensional motion. 



An interesting note on the colouring matter of red 

 torulae, by Mr. A. C. Chapman, appears in the 

 Biochemical Journal for December, 1916. Study of 

 this colouring matter showed that it resembles car- 

 rotene in being practically insoluble in water, in 

 dissolving to a blue solution in concentrated sulphuric 

 acid, and in the fact that its chlorotorm solution, 

 when warmed and exposed to the light, quickly 

 becomes colourless. But cxjmparison of the absorption 

 spectrum of the torulae colouring matter with that of 

 carrotene showed that the two are by no means 

 identical. 



The Journal of the Franklin Institute for March 

 contains the address delivered before the institute 

 in October last by Prof. L. V. King, of McGill 

 University, on the acoustic efficiency of fog-signal 

 machinery. After a review of the work on fog signal- 

 ling done by the committee of the Trinity House in 

 this country and by the lighthouse boards of the 

 United States and of France, he describes his own 

 measurements made in 19 13 in connection with the 

 fog-signal plant at Father Point, Quebec. The sound- 

 producer thtere is a compressed-air siren of the 

 Northey type using air at 25 lb. per square inch and 

 giving a note of frequency 180 per second. During 

 the actual emission of the sound 100 horse power is 

 used. By measurement of the temperature of the 

 issuing air when sound was produced and when not, 

 it was found that only about 24 horse power was 

 converted into sound. Tests of the intensity of the 

 sound received at points on the water up to eight miles 

 from the source were made by means of the sound- 

 meter of Prof. A. G. Webster, of Clarke University, 

 which depends on the motion of a small mirror 

 mounted on a mica diaphragm at one end of a 

 resonator. Zones of silence were found, on both 

 sides of which the sound was distinctly heard. The 



NO. 2476, VOL. 99] 



existence of these zones appears to be intimately 

 connected with the direction of the wind and to a 

 less extent with the weather. 



Prof. Martin Knudsen has recently described some 

 interesting experiments on the condensation of metallic 

 vapours on cold bodies (Oversigt Kgl. Danske 

 Vidensk. Selsk. Fork., 1916, No. 4, p. 303). When 

 mercury vapour passes through a narrow opening into 

 a large glass bulb containing a concentric smaller 

 bulb tube with liquid air, most of the mercury vapour 

 is condensed on the front of the smaller bulb facing 

 the opening; a little passes alongside it on to the 

 inner surface of the larger bulb, but no mercury is 

 condensed on the back of the smaller bulb nor behind 

 it on the larger one. The bulb with liquid air casts, 

 as it were, a shadow, and retains all the molecules 

 striking it. If, on the other hand, the inner bulb is 

 only cooled with ether and carbon dioxide, the greater 

 portion of the mercury vapour is not retained by it, and 

 is condensed on the front half of the larger bulb. 

 From the weight of mercury so condensed on the 

 latter in an interval of time during which the inner 

 bulb has only acquired a deposit thinner than the 

 (known) limit of visibility, it is calculated that the 

 chance of a mercury molecule being retained at its 

 first impact on a glass surface at —77-5° is less than 

 I in 5000. Between this temperature and that of liquid 

 air there is a critical temperature in the neighbouj-hood 

 of —140° to —130°. Preliminary experiments with a 

 simpler apparatus indicate that for zinc, cadmium, and 

 magnesium this critical temperature lies between 

 — 183° and —78°, for copper between 350° and 575°," 

 and for silver above 575°. 



Although the principles that render colour kine- 

 matography possible are so simple, there appears to 

 be an inexhaustible field for inventors in the applica- 

 tions of these principles, and not infrequently the 

 details of "new" processes appear to the student of 

 science as disadvantageous complications, if not actual 

 infringements, of the necessary conditions. However, 

 processes stand or fall by their results, and the 

 Scientific American of March 10 states that the last 

 "new process," as demonstrated at the American 

 Museum of Natural History and the New York 

 Academy of Sciences, seems to be "perfection." The 

 1 simple attachments necessary can be fitted to any 

 ! apparatus. A single film is used, and the pictures 

 j are taken behind a revolving four-sector colour filter, 

 i arranged with two pairs of complementary colours — ■ 

 j namely, blue and orange, and blue-green and red. 

 The complete element consists, therefore, of four 

 i consecutive pictures taken through colour filters in 

 the order just named. The colour filter for pro- 

 1 jection has only two colours, red and blue, and has 

 ! therefore to rotate at twice the rate of the filter disc 

 ; used for taking the photographs. But each colour 

 j filter in the projector disc is subdivided into three 

 sectors in such a way that each red and orange 

 j picture is projected through a red filter increasing 

 I in intensity in three stages, and each blue and blue- 

 i green picture in a similar way through three blue 

 filters. The usual rate of projection is sixteen pic- 

 tures per second, and Mr. G. A. Smith, in his 

 " Kinemacolor," introduced in 1907, who used two 

 consecutive colour pictures, found it necessary, as 

 seems natural, to double this rate so as to maintain 

 the same rate for each complete element. la the 

 present case, with a quadruple element, one might 

 expect the rate to be increased to four times — namely, 

 sixty-four per second — but the actual rate stated is 

 twenty-four — that is, only six complete elements per 

 second. 



