is: 



KNOWLEDGE. 



May, 1915. 



METEOROLOGY. 



Bj Wmii \m Marriott, l-.R Mi r.Soi 



III1-: WEATHER OF MAY.— The month oi May is 



gem-rally characterised by a great increase ol warmth and 

 sunshine, while the still increasing power of the Sim's rays 



tnifests itselt by the rapid advance oi vegetation. May 

 is, however, subject to groat vicissitudes of temperature, 

 and sometimes sharp frosts occur at night, which seriously 

 injure the fruit and cereal crops. 



•• Till May be out 

 Leave not off a clout.'' 



.Ma\ was a vcrj cold month in the years 1845, 1855, 

 1856, 1877, 1879, 1885, and 1902 ; and it was very warm in 

 the years 1841, 1848, 1865, 1868, 1893. and 1895 



The average mean temperature at Greenwich for May 



is 53 -0 ; in 1S4S it was as high as 59° -7, while in 1879 it 

 was as low as 48° -6. The average maximum temperature 

 is 63°-9; the highest mean was 73° -3 in 1848, and the 

 lowest 57 -3 111 1902. The average minimum temperature 

 i- -13 -7; the highest mean was 48° -3 in 1841, and the 

 lowest 39 -2 m 1876. The absolute highest temperature 

 recorded was 87 -5 in 1880 on the 26th, and the absolute 

 lowest was 28°-l in 1877 on the 4th. The latest date on 

 which a temperature below 32° was registered was on 

 the 24th in I8H7. 



The average rainfall for the month of May is 1 -95 inches ; 

 the greatest amount was 4-37 inches in 1865, and the least 

 0-25 inch in 1833. The heaviest fall in one day was 1-40 

 inches in 1825 on the 13th. The average number of " rain 

 ■ lays " (i.e., on which 0-01 inch fell) is 12-4 : the greatest 

 number of days was twenty-two in 1902, and the least 

 three in 1848. The average amount of bright sunshine at 

 the Kew Observatory, Richmond, is two hundred hours. 



The average barometric pressure in London for May is 

 29-969 inches ; the highest mean was 30-227 inches in 1896, 

 and the lowest mean was 29-790 inches in 1891. 



CYCLONES AND ANTICYCLONES.— It will be remem- 

 bered that it was proposed to hold a Meteorological 

 O inference in Edinburgh in September last, but owing to the 

 war it had to be postponed. Two or three papers which were 

 to have been read at the Conference have now been printed 

 in The Journal of the Scottish Meteorological Society. One 

 of these, on " Cyclones and Anticyclones." is by Mr. W. H. 

 Dines, F.R.S., and in this he points out that the old convec- 

 tional theory of the cyclone, known as " Ferrel's Theory," 

 is utterly untenable in view of recent knowledge. 

 Observations obtained by means of registering balloons 

 have led to the definite conclusion that the lower strata of 

 the atmosphere are relatively cold in cyclones and relativelv 

 warm in anticyclones. The statistical treatment of the 

 observations has led to certain other conclusions, and shows 

 that there is a very intimate connection between the 

 temperature and the pressure of the upper air, but that, 

 except close to the surface, there is very little connection 

 between the temperature of the air and its direction or rate 

 of motion. The importance of the pressure at a height of 

 about nine kilometres is demonstrated, and an explanation 

 is given of the way in which the temperature conditions in 

 cyclones and anticyclones follow naturally from the dis- 

 tribution of pressure of nine kilometres. Mr. Dines further 

 points out that the effect of radiation is of secondary import- 

 ance in altering the temperature of the air. 



TORNADO IN WALES, OCTOBER 27th, 1913. 



Reference was made in " Knowledge " (Volume XXXVI, 

 page 465) to the remarkable storm of a tornado type which 

 occurred in South Wales on October 27th, 1913. The 

 Meteorological Office has published, in The Geophysical 

 Memoirs, a report on this tornado by Mr. H. Billett who 

 spent three days in visiting the greater part of the region 

 affected by the storm. A system of violent meteorological 

 phenomena passed along a line running almost due north 

 from the south of Devon to Cheshire, between 3.45 and 



9 p.m. There appear to have been four main regions of 

 ai lion in its path, namely, (1) South Devon, (2) South 

 Wales, (3) Shropshire, and (4) Cheshire ; the most violent 

 was that in the Tall \ alley. One of the most remarkable 

 features of the storm was the sharpness of its boundaries 

 on either side of its track. Practically no damage was done 

 outside the narrow limits of the course, which nowhere 

 exceeded one thousand feet in width. The tornado was 

 accompanied by very severe lightning and torrential rain- 

 fall, and reached its greatest force at Abercynon and 

 Edwardsville, where five deaths occurred. The storm was 

 circular in shape ; and, as it progressed with a speed of 

 thirty-six miles per hour, its duration at any place, assuming 

 the width of the track within which damage was done to be 

 three hundred yards, works out at seventeen seconds. The 

 evidence collected shows that the storm was a genuine 

 tornado of the type common enough in parts of America, 

 but fortunately of rare occurrence in this country. 



MIRAGE ON THE CORNISH COAST.— Mr. P. H. 

 Horton in a letter to The Times gave a graphic account of 

 a curious phenomenon which he saw from the Cornish coast 

 at Mawnan, a few miles from Falmouth, for about half an 

 hour on the afternoon of October 24th. In a shallow cloud- 

 bank, stretching across the horizon from south-east to 

 south, there gradually appeared what seemed to be a line 

 of coast, with woods, trees, fields, hedges, and houses in 

 their natural colours. At first he thought it was merely 

 a peculiar arrangement of clouds, but soon he recognised 

 that it was a complete reflected panorama of the coast, 

 and he gradually identified St. Keverne, with its church 

 spire, the Helford River, Mawnan Church, Rosemullion, 

 Falmouth Harbour, and St. Anthony. Shortly before the 

 whole scene faded away a reflection of Pendennis Head, with 

 the Castle and the military huts, emerging like some huge 

 ship from a fog bank, appeared most distinctly, and was 

 visible for several minutes. Every detail of the whole 

 scene was reversed as in a looking-glass, and slightly 

 magnified ; for, although the panorama seemed to be some 

 twenty miles away, everything appeared as it would to an 

 observer from the distance of only a mile or so. The colours 

 were a little less bright than those of the real coast at the 

 time. Mr. Horton adds that the scene, as a whole, was 

 visible all the time, but the details of a small portion only 

 were quite distinct at any one time, commencing in the 

 south and gradually moving towards the east, the effect 

 being that of a powerful searchlight being very slowly 

 turned from right to left on to the opposite shore of a large 

 lake. 



MICROSCOPY. 



By F.R.M.S. 



NEW METHOD OF STAINING RADULAE.— Figure 

 126 on page 147 shows the radula of Zonites olivetorum of 

 Moquin-Tandon.of which I took several specimens in August, 

 1897, near the top of the Col de 'fillet (Hautes- Pyrenees). We 

 have no British form with a radula of this type, but it may 

 be compared to Politti nitidula. The figure is introduced 

 here in order to show the advantage gained by staining 

 the radula with a suitable stain and mounting in Canada 

 balsam, the refractive index of which is nearly the same as 

 that of the chitin of the radula, while it is also in corre- 

 spondence with the optical system of the microscope. Thus 

 the picture seen on the stage is entirely due to the stain, 

 and contains no fallacious shadows representing difference 

 of refractive indices. The resolution in depth is the maxi- 

 mum possible without distortion of the elements of the 

 picture. The photograph was taken with an objective of 

 N.A. 0-18, and the structures are large. 



The method adopted is as follows : — 



(1) Boil out the radula with one or two per cent, 

 caustic potash, wash, and neutralise with dilute 

 acetic acid. 



