June 7, 19 17] 



NATURE 



295 



most places in the north of Scotland, where the 

 average excess was about 05° F. At Bath the defici- 

 ency amounted to 5° January had a deficiency over 

 the whole of the United Kingdom, the defect being 

 greatest in the midland, southern, and western parts 

 of England and in Ireland, exceeding 5° in a few 

 places. February had a slight excess of temperature 

 in the Shetlands, Orkneys, and Hebrides ; elsewhere 

 it was deficient, the deficiency exceeding 7° at Here- 

 ford, and being more than 5° at many places in 

 different parts of England and at a few places in the south 

 of Ireland. March had a deficiency of temperature 

 over the entire area of the British Islands, exceeding 

 5^ at some places in the midland and eastern districts 

 of England. April was everywhere cold, the deficiency 

 of temperature exceeding 5° in many parts, and 

 amounting to 6-6° at Aspatria, in Cumberland. 



London is represented by eight stations, including 

 Greenwich and Kew Observatories. The mean tem- 

 perature, the arithmetical mean of the maximum 

 and minimum readings, from the eight stations for the 

 five months December, 1916, to April, 1917, is 380'^, 

 which is 36° below the average for the whole period. 

 The highest of the several means for London was 

 39-3° at South Kensington, the observing station of 

 the Meteorological Office, and the lowest Hampstead, 

 35-9°. The mean of the minimum, or night, readings 

 at Hampstead was below the freezing point in each 

 of the months from December to March, and in April 

 the mean minimum was 33°. At Greenwich the mean 

 of the maximum for the five months was 433°, the 

 mean of the minimum 323°, and the mean was 37-8°, 

 which is 38° below the normal. The means for 

 January and February were both 35-3°, and April, with 

 a mean of 427°, had a deficiency of 45°, the greatest 

 deficiency from the normal in any of the five months. 

 The mean temperature for the five months was 02° 

 higher than for the corresponding period from Decem- 

 ber, 1890, to April, 1891, and it was o-i° lower than 

 for December, 1878, to April, 1879, the next lowest 

 mean since 1841, and 02° lower than from December, 

 1844, to April, 1845. 



Taking six representative stations in the midlands, 

 for the five months the mean temperature was 36-8°, 

 and the difference from the normal was minus 39°. 

 At Brighton the mean temperature was 386°, a de- 

 ficiency of 3-9° from the average. In Dublin the 

 mean temperature for the five months was 400°, and 

 the deficiency 35° ; at Jersey 40-7°, and deficiency 42°. 

 Three representative stations for Scotland give the 

 mean temperature 379°, and the mean deficiency from 

 the average was 23°. 



Meteorological information from western and 

 northern Europe shows that other parts were similarly 

 affected with prolonged cold. 



Dr. Mill, of the British Rainfall Organisation, in a 

 letter to the Times of June 4, directs attention to the 

 month which has just closed as being the warmest May 

 at Camden Square, London, since the establishment 

 of observations in 1858. He gives the mean tempera- 

 ture on a Glaisher stand as 59- 1° F., or 51° above the 

 average, whilst April was just 5° below its average. 

 At Camden Square, May, 1868, "had a mean tempera- 

 ture 589°, a trifle cooler than the recent May, and 

 it was followed by a very hot summer. Dr. - Mill 

 quotes several warmer Mays according to the old 

 London records, and mentions that onlv in 1809 <^i^ 

 an extremely warm May follow, as this vear, an 

 extremely cold .\pril. At South Kensington^ the ob- 

 senang station of the Meteorological Office, the mean 

 temperature in a Stevenson's screen for May was 

 59-6°. The Greenwich observations give 588° in 1841 

 and 1848 as the previous highest May temperatures, 

 from maximum nnd minimum readings, since 1841, ' 

 NO. 2484, VOL. 99] 



and in 1893 the mean was 58-4°, In 1908 at Green- 

 wich the mean temperature for April was 44-3°, which 

 is 4° below the average, whilst that for May was 56-7°, 

 or 3° above the average. The fallowing summer was 

 bv no means fine or hot. Chas. H.arding. 



THE COOLIDGE X-RAY TUBE. 



THE Coolidge X-ray tube has been on its trial in 

 this country during the last two years, and it 

 may be said wi;h some confidence that it has gone 

 a very long way towards justifying the claims which 

 have been made concerning it. Whether the tube be 

 judged from the laboratory or from the clinical point 

 of view, it marks a new era in the history of the 

 X-ray tube. There is now to the hand of the experi- 

 menter or of the radiologist a source which provides 

 him with a beam of X-rays which can be varied in the 

 course of a few seconds, as regards both quality and 

 output, over a very wide range; such radiation, more- 

 over, may be repeated with certainty. 



The work of Sir E. Rutherford and his colleagues, 

 which was directed to find the shortest wave-length of 

 the radiation emitted by the Coolidge tube, disclosed 

 the fact that a limit was set to the penetrating power 

 of this radiation when the potential difference between 

 the terminals of the tube was about 150,000 volts. 

 The Coolidge tube can be run at a higher working 

 voltage than the ordinary X-ray tube owing to the 

 absence of any measurable quantity of gas within the 

 former, and the range of radiation emitted by it ex- 

 tends rather further into the region of the shorter 

 wave-lengths than is obtained with the older type of 

 tube. 



There is a considerable clinical use of such very 

 penetrating rays, which are rather more penetrating 

 than the 7 rays from radium-B, but less so than those 

 emitted by radium-C. The difficulty of protecting 

 those who apply such radiation is considerable, but 

 the necessity for so doing is no less urgent than it is 

 apparent, and we are glad to see that prominence is 

 given to this question in a descriptive leaflet of the 

 Coolidge tube, dated October 31, 19 16, issued by the 

 British Thomson-Houston Co., Ltd. 



This memorandum contains a description of the 

 tube, its mode of construction, and the methods which 

 are now generally employed in its manipulation, both 

 for radiographic and for radio-therapeutic work. 



Considering the ease with which the Coolidge tube 

 may be manipulated, and the short time which is re- 

 quired by anyone conversant with X-ray matters to 

 acquire the necessary- technique, it must be inferred 

 that the only hindrance to its more general adoption 

 in this country is the high cost of the tube. 



The Coolidge tube may perhaps be looked upon as 

 the most successful practical application which has vet 

 been made of the classical work of Prof. O. W. 

 Richardson on thermionic currents. We trust that the 

 British Thomson-Houston Co.. Ltd., which states that 

 it is the owner of the English patents of this tube, will 

 be instrumental in putting the Coolidge X-rav tube 

 within the reach of a wider public than exists to-dav. 



THE ROYAL OBSERVATORY, 

 GREENWICH. 



THE report of the Astronomer Royal to the Board of 

 Visitors of t"he Royal Observatory, Greenwich, 

 was presented at the annual visitation of the Obser\*a- 

 tory on June i. A few of the matters dealt with in the 

 report are here summarised. 



The catalogue of stars down to 90m. on the B.D. 

 scale between the limits of 24° and 32° of north de- 

 clination has been completed by the determination of 



