August 3, 19 16] 



NATURE 



471 



Atlantic, the weather was abnormally warm in 

 January. 



The rainfall maps of Australia for 1915, prepared 

 by Mr. H. A. Hunt, Commonwealth meteorologist, 

 have been published. A large map shows the dis- 

 tribution of rainfall for the year, and a number of 

 smaller maps, printed on the back, give the rainfall 

 for each month. The year was characterised by an 

 unusual amount of rainfall in the western part of the 

 continent, which in some parts was the heaviest on 

 record. On the other hand, the drought conditions 

 in Queensland were the most severe ever experienced 

 in that State. There were great losses of stock, and 

 the sugar crops in the east coastal districts, as well 

 as many of the cereal crops on the downs, were every- 

 where a failure. In the southern wheat belt, how- 

 ever, the conditions of rainfall were all that could be 

 desired. Accompanying these well-sustained rains 

 another important factor was the exceptionally mild 

 winter, with a June and July temperature for the 

 continent about 2^° above the normal. Probably the 

 wheatlands of Australia never before experienced such 

 favourable conditions of temperature and rainfall, 

 and the result was a record harvest. The comparison 

 with the previous year was most marked, for 1914 

 was a year of drought in South Australia and the 

 Riverina. 



The Quarterly Review for July contains an article 

 by Dr. Charles Davison on the sound of big guns. 

 The author has collected together those accounts of 

 the propagation of the sounds of big guns to great 

 distances which are sufficiently numerous and well- 

 authenticated to provide a basis for generalisations on 

 the subject. The firing at Waterloo appears to have 

 been heard in Kent, 140 miles away, and that when 

 the Alabama w-as sunk by the Kearsarge in 1864, 125 

 miles away. The guns fired at the Naval Review in 

 1897 were heard 135 miles away, and the minute-guns 

 fired at the funeral of Queen Victoria in 190 1, 13^^ 

 miles away. In all cases the audibility was greatest 

 down the wind, owing, as Sir George Stokes showed 

 sixty years ago, to the bending of the sound-waves 

 downward by the greater speed of the wind as the 

 height above the ground increases. The remarkable 

 zones of silence which sometimes intervene between 

 stations near the guns and the more distant points at 

 which the sounds are heard are equally well explained 

 by the existence of local winds blowing towards the 

 source of sound and tilting up the sound-wave above 

 the heads of the listeners. The author makes no 

 reference to the approximate equality of the maximum 

 distances a century ago and now when the g^ns are 

 much larger, although this requires explanation. 



At the present time, when the production of glass 

 apparatus for scientific and technical purposes is 

 receiving special notice in this country, attention may 

 be directed to Circular No. 9 of the United States 

 Bureau of Standards, which deals with the testing 

 of glass volumetric apparatus. It is draw-n up, no 

 doubt, with a view to American requirements, but 

 the principles involved are of general application. 

 For the assistance of manufacturers specifications are 

 given respecting the construction of glass instruments, 

 such as measuring flasks, cylinders, pipettes, burettes, 

 specific gravity bottles, and " Babcock "' bottles for 

 milk analysis. The information indicates the re- 

 quirements of the Bureau as to the dimensions, de- 

 signs, and types of vessels which are suitable for 

 standardisation, and describes how the graduation of 

 them should be carried out, with the limits of error 

 which are tolerated in the calibration. Useful hints 

 may be gathered from the circular bv manufacturers 

 who are taking up the industry in question. 

 NO. 2440, VOL. 97T 



OUR ASTRONOMICAL COLUMN. 



MO.NOCHROMATIC PHOTOGRAPHS OF PlANETS. — Prof. 



R. W. Wood has given an account of further results 

 obtained by the photography of celestial bodies through 

 filters transmitting limited regions of the sj>ectrum 

 {Astrophysical Journal, vol xliii., p. 310). After much 

 preliminary work, successful photographs were readily 

 obtained when the 60-in. reflector at Mount Wilson 

 was placed at his disposal for four nights during last 

 October. For the ultra-violet filter a bromine cell 

 was used, transmitting the region from 3500 to the 

 end of the solar spectrum at 2900; the infra-red 

 screen transmitted the region above 7000, the yellow 

 screen all rays above 5000, and the violet from 4000 

 to 4500. In the case of Saturn the pictures taken 

 through the infra-red screen only showed the merest 

 traces of the belts ordinarily seen, while through the 

 yellow screen the planet presented its usual appear- 

 ance. On the plates taken with violet light a very 

 broad, dark belt surrounded the planet's equator, and 

 a dark cap of consitlerable size was shown about the 

 pole. These features were also present in ultra-violet 

 light, but were less pronounced; they may possibly be 

 due to the existence in the planet's atmosphere of some 

 substance capable of absorbing violet and ultra-violet 

 light. Another point of interest was a decrease in 

 contrast between the inner and outer ring as the wave- 

 length of the effective light decreased, suggesting that 

 the outer ring contains so much finely divided matter 

 that it shines in part by diffusion. In the case of 

 Jupiter, the dark belts were scarcely visible on the 

 infra-red plates, while they were shown in greatest 

 contrast with violet light. The dark polar cap shaded 

 off gradually in the yellow and infra-red pictures, but 

 was sharply terminated in the violet and ultra-violet 

 photographs. It is hoped that it may be possible to 

 investigate the surface of Mars by this method at the 

 next near approach to the earth. 



The Polar Caps of Mars and Solar Radlatiox. — 

 An interesting investigation of the rate of melting of 

 the polar caps of Mars in relation to the sun-spot 

 period has been made by M. Antoniadi. An examina- 

 tion of the records of the planet from 1862 to 1914 

 has shown that, in general, the polar caps melt more 

 rapidly at times of great solar activity than when solar 

 activity is feeble. Out of twenty-one series of observa- 

 tions during the period in question, .no fewer than 

 seventeen were definitely in favour of this conclusion, 

 and only four unfavourable. Two of the exceptions 

 were the oppositions of 1862 and 1873, when the melt- 

 ing of the caps was normal, in spite of considerable solar 

 activity; another was in 1877, when rapid melting 

 occurred with feeble solar activity; and the fourth in 

 1886, when rapid melting was associated with only 

 moderate solar activity. The slowest recorded shrink- 

 age of the caps accompanied the prolonged sun-spot 

 minimum of three years ago, while one of the most 

 rapid rates of melting coincided with great spot 

 activity in 1894. M. Antoniadi's conclusion is in satis- 

 factory agreement with the now generally accepted 

 view that solar radiation is greatest at times of sun- 

 spot maximum, and with the supposition that the 

 polar caps of Mars are very thin, and consequently 

 very sensitive to variations of temperature (Roval 

 Astronomical Society, June). 



Variable Stars near the Solth Pole. — In con- 

 tinuation of the search for variables on photographs 

 covering the entire sky. Miss Leavitt has examined 

 plates of the stars near the South Pole, and has dis- 

 covered nineteen new variables in that region. One 

 of them is apparently of the Algol type, having a 

 normal magnitude in and a minimum of 10-6 (Har- 

 vard Circular 191). 



