524 



NATURE 



[March 28, 1889 



and also Pouillet's direct pyrheliometer, which consists of a 

 •cylindrical box of steel filled with mercury, into which the bulb 

 of a thermometer is introduced, the stem being protected by a 

 piece of brass tubing. As the surface on which the sun's rays 

 fall and the quantity of mercury in the cylinder are both known, 

 the effect of the sun's heat upon a given area can be expressed 

 by stating that it is competent in five minutes to raise so much 

 mercury so many degrees in temperature. The Rev. F. W. 

 Stow showed an improved form of Pouillet's pyrheliometer, in 

 which the instrument is placed in a silvered tube to shield it 

 from wind and from all solar rays, except when the tube is 

 turned directly towards the sun. Mr. Casella exhibited Secchi's 

 solar intensity apparatus, in which two thermometers are kept 

 immersed in a liquid at any convenient temperature, and a 

 third, of which the stem passes through the same liquid and the 

 bulb is outside it, is exposed to the rays of the sun shining down 

 -the hollow cylinder. The increase of temperature thus obtained 

 is found to be the same, independent of the temperature of the 

 liquid which surrounds the thermometer. 



The British Association Solar Radiation Committee showed 

 Prof. Balfour Stewart's actinometer ; and Dr. Angstrom, of 

 Stockholm, sent one of his pyrheliometers and a photograph of 

 another pattern. 



Luvini's dietheroscope for observing the changes of atmo- 

 spheric refraction optically, and Bellani's lucimeter, as arranged 

 by Prof. G. Cantoni for use at the Italian meteorological stations, 

 were exhibited by the Meteorological Council ; and Mr. Hicks 

 showed S')me of Crookes's radiometers. 



Dr. A. D jwnes illustrated his method of slow actinometry by 

 oxalic acid, in which a definite quantity of a standard solution 

 of oxalic acid is exposed to the action of light for a definite 

 period ; subsequently it is used to bleach a standard solution of 

 .permanganate of potash. The quantity of oxidized oxalic acid 

 solution, compared with the quantity originally required to 

 produce the same effect, is a measure of the intensity of the 

 light. 



Engravings illustrating Violle's, Crova's, and Frolich's 

 actinometers were also exhibited. 



The solar radiation thermometer consists of an ordinary 

 maximum thermometer, with the bulb and about one inch of the 

 stem coated with lamp-black, inclosed in a glass shield exhausted 

 of air. Various specimens of this instrument were exhibited, with 

 arrangements for testing the degree of exhaustion. Hicks's 

 black bulb maximum thermometer in vacuo is supplied with 

 platinum wires and a battery for testing the vacuum, while 

 Negretti and Zambra's has a mercurial test gauge. Mr. Hicks 

 also showed one of these instruments which had at the end of 

 the outer jacket a second chamber in which is mounted one of 

 ■Crookes's radiometers for testing the vacuum. 



The Royal Meteorological Society showed a pair of black- 

 bulb and bright-bulb maximum thermometers in vactio as 

 recommended for use at the Society's stations ; while Messrs. 

 Negretti and Zambra exhibited a similar pair of thermometers 

 mounted in an upright position with the bulbs uppermost, as 

 used at the Montsouris Observatory, Paris. 



Mr. Casella showed Southall's helio-pyrometer for testing 

 the accumulated heat of the sun in a confined blackened space, 

 under glass. A black-bulb maximum thermometer is fixed on a 

 cushion at the bottom of a box, the sides of which are also 

 cushioned, and a thick piece of plate-glass is laid upon the top 

 to prevent currents of air carrying off the heat. The box is 

 placed in such a position that the sun's rays may strike as nearly 

 as possible perpendicularly on the glass, when water contained 

 in a small vessel will boil violently in the box. 



The practical working of sunshine recorders may be said 

 to date from 1854, when Mr. J. F. Campbell mounted a hollow 

 glass sphere filled with acidulated water in the centre of a bowl 

 of mahogany so arranged that the sun's rays were focussed on the 

 interior of the bowl and burned it. The lines of burning 

 therefore indicated the existence of sunshine. Solid glass 

 spheres were substituted for the hollow ones in 1857, and in 

 1875 cards in metal frames were substituted for the wood. The 

 Meteorological Council exhibited a number of wooden bowls 

 showing the effect of sunshine by burning in the years 1855-56, 

 1883-84, and 1887-88 ; and the Astronomer-Royal sent the sun- 

 shine recorder with a hemispherical metal bowl which was in use 

 at the Royal Observatory, Greenwich, from 1876-86. Specimens 

 of the Campbell sunshine recorder with the improved Stokes's 

 zodiacal frame for a fixed latitude, were shown by the Meteoro- 

 logical Council ; a recorder with adjustments for use in any 



latitude, by Messrs. Negretti and Zambra ; and the Whipple- 

 Casella sunshine recorder, by Mr. Casella. 



Mr. Jordan exhibited an experimental instrument for record- 

 ing the intensity of daylight, the results being obtained by 

 revolving a disk of sensitized paper behind a screen with a 

 rectangular aperture. Messrs. Negretti and Zambra showed the 

 various patterns of Jordan's photographic sunshine recorder, 

 which consists of a cylindrical box, on the inside of which is 

 placed a slip of cyanotype paper. Sunlight being admitted into 

 this chamber by three small apertures, is received on the paper, 

 and travelling over it by reason of the earth's rotation, leaves a 

 distinct trace of chemical action. In the second pattern of this 

 instrument two apertures are used instead of three ; while in 

 the new pattern two semi-cylindrical boxes are employed, one 

 to contain the morning and the other the afternoon record. 

 Prof. McLeod's photographic sunshine recorder was exhibited 

 by Mr. Hicks. This consists of a glass sphere silvered inside 

 and placed before the lens of a camera, the axis of the 

 instrument being placed parallel to the polar axis of the earth. 

 The light from the sun is reflected from the sphere, and some 

 of it passing through the lens forms an image on a piece of 

 sensitized paper within the camera. 



Mr. A. S. Marriott showed two patterns of his instrument for 

 comparing the active value of light at different stations ; and the 

 Kew Committee sent the chemical photometer devised by Sir 

 Henry Roscoe. 



Among the new instruments exhibited were Fineman's and 

 Galton's nephoscopes for observing the direction of motion of 

 clouds ; Davis's improved air meters ; Negretti and Zambra's 

 recording hygrometer ; Casella's Boylean-Mariotte barometer ; 

 and de Normanville's self-compensating sympiesometer. Mr. 

 Murday showed in action his apparatus for obtaining readings of 

 an aneroid placed at a distance by means of electric currents. 

 An instrument, called the stephanome, which is used at the 

 Ben Nevis Observatory for measuring the angular sue. of halos, 

 fog-bows, glories, &c., was also exhibited. 



Mr. Clayden showed a very ingenious and instructive working 

 model illustrating the generation of ocean currents, which was 

 a great attraction to all the visitors at the Exhibition. This 

 model shows how the prevalent winds over the Atlantic are the 

 chief cause of the circulation of the waters. A number of tubes 

 are so arranged that when an attached blower is worked the 

 circulation of air produced resembles that of the atmosphere ; 

 the imitation winds thus set up react upon the surface of the 

 water, creating a system of currents which reproduces the main 

 features observed in the Atlantic. Special attention was drawn 

 to the Gulf Stream issuing from the Gulf of Mexico, and to the 

 return current flowing eastwards between the equatorial currents. 

 Mr. Clayden also showed some lantern slides illustrating the 

 spiral circulation of the wind in both a cyclone and an anticyclone. 



One of the chief features of last year's Exhibition was the 

 large collection of photographs of flashes of lightning which had 

 been gathered together by the Royal Meteorological Society 

 from all parts of the world ; this year the Society exhibited a 

 number of similar photographs which have been received since 

 May 1888. Near to these were placed a number of photographs 

 of the electric spark taken by Mr. Wimshurst when the sensitive 

 plate was rotating 2500 times per minute. These flashes are 

 quite sharp and distinct, and show no sign of the movement of 

 the plate. 



A very interesting and valuable collection of sixteen photo- 

 graphs taken on the summit of Ben Nevis during the last eleven 

 months were exhibited by the Directors of the Observatory, of 

 which the following were of special interest : (i) cirrus cloud at 

 the northern horizon, taken at midnight at the time of the 

 summer solstice when the clouds are seen brightly illuminated ; 

 (2) St. Elmo's fire, at 11 p.m., on the top of the stove-pipe ; 

 and (3) views of the Observatory after continued fog and strong 

 wind, but no fall of snow, when everything is covered with long 

 crystals of ice formed out of the fog. 



Mr. Bromhead exhibited two large photographs showing the 

 thick rime on trees at Lincoln oa January 7 last ; and Mr. 

 H. P. Curtis showed a photograph taken by moonlight. 



Photographs of clouds were exhibited by Captain Wilson- 

 Barker, Mr. Shepherd, and Captain Maclear. 



The Exhibition also included a number of photographs and 

 drawings of instruments, &c., as well as some models of hailstones, 

 7 inches in circumference, which fell near Montereau, France, 

 on August 15, 1888. 



William Marriott. 



