August iS, 1910] 



NATURE 



21 



body of the catalogue. The nine sections include 

 mochanical engineering, electricity, civil engineering, agri- 

 culture, horticulture and arboriculture, food products, 

 mining and metallurgy, textile industries, and chemical 

 industries. :\ plan at the end shows the positions of the 

 stands of the various exhibitors. 



The Physikalische Zeitschrift for August i contains a 

 review of the present state of our knowledge of the proper- 

 ties of the a particles sent out by radio-active substances, 

 by Dr. H. Geiger, of Manchester. The velocity of the 

 homogeneous rays sent out by radium C appears to be 

 2o5xio° centimetres per second, and the quotient of the 

 electric charge by the mass 5-07x10' electromagnetic units. 

 The mean number of a particles sent out by a gram of 

 radium per second is 3-1x10'°, and each carries a charge 

 ()-3 to g-6xio-'° electrostatic units, and appears to be a 

 helium atom. The progress of each is checked by the 

 inolecules of a gas, and in air the path described does not 

 i-xceed a few centimetres in length. During the descrip- 

 tion of this path each is capable of producing 1.72X10° 

 ions by collision. The results of the recent measurements 

 of the diminution of the velocity of the particles as they 

 pass through solids, their scattering, and their ultimate 

 absorption are all discussed in a clear and thorough 

 manner. 



.\ LETTER from Sir William Ramsay, iii the Chemical 

 XcK's of .August 5, directs attention to a new fact in the 

 history of the development of the Leblanc process for the 

 manufacture of soda. It has generally been believed that 

 I.eblanc perfected a process devised by De La M^therie in 

 1789. A letter to Dr. Black, written by a Mr. Geo. 

 (iolder, of Edinburgh, and dated March 19, 1782, shows, 

 however, that the black ash process had already been 

 devised and patented by an English inventor named 

 Collinson. A specimen of black ash prepared by Collin- 

 son's process was submitted to Dr. Black, who reported 

 that it contained " more alkali than the best .Alicant 

 Barilla in the proportion of 68 to 44, and more than the 

 best kelp in the ratio 68 to 10." " It is an excellent 

 ash for the soap-boilers . . . and there is no need to use 

 lime in drawing the leys from it, as it is already in a 

 caustic state." " -After this," the writer adds, " there 

 appears little doubt who invented the black-ash furnace." 



Manv examples of smoky chimneys are no doubt owing 

 to carelessness and lack of knowledge in those concerned 

 with the work, but we also find many architects and 

 builders of repute being occasionally nonplussed by the 

 problem. Some important points in chimney design are 

 given in the Builder for -August 13. The grate should be 

 provided with a blower to induce a good draught at the 

 start. The flue should be expanded laterally to a width of 

 about 2 feet a short distance above the grate, and then 

 brought in again, forming what is usually termed a 

 " bottle." .Above this, one or two bends of about 150 

 degrees should be made. The top should be slightly con- 

 tracted, and the chimney-cap sloped up sharply all round 

 the aperture or pot ; outside chimneys should be avoided ; 

 stacks should come as near the highest part of the roof 

 as practicable ; a number of flues should not be packed 

 too closely together in a large stack, but kept as distinct 

 as possible ; the outer walls of stacks should be 9 inches 

 thick. 



In an article on the International Road Congress, which 



opened in Brussels on August i, Engineering for August 12 



gives the altered form of a rejected resolution, which in 



its original form condemned macadam. The resolution 



NO. 2129, VOL. 84] 



finally adopted is as follows : — " Macadam, carried out by 

 the methods of Tresaguet and Macadam, causes dust and 

 mud, is expensive to maintain, and is suitable in large 

 cities only for streets where the traflic is not very great 

 or heavy. The experimental work carried out in recent 

 years with macadam, improved by using a bituminous or 

 tarry coating or binder, ought to be continued to deter- 

 mine the best method of utilising this kind of construction 

 under varying conditions, and the results considered at the 

 ne.xt congress." Our contemporary directs attention to a 

 point which requires scientific investigation, viz. the exact 

 behaviour of a sand foundation under stone pavement. 

 On the Continent, a bed of sand from 3 inches to 6 inches 

 deep is almost invariably used, and the setts are bedded 

 directly on and in the sand. The sand is spoken of as a 

 " cushion," and is said to be elastic. Another view is 

 that it absorbs the shock on the pavement, saves the 

 stones from damage, and reduces the noise of traffic. It 

 would be easy to settle the points in doubt by experiments 

 in an engineering laboratory. 



OUR ASTROXOMICAL COLUMN. 



A New Comet. — A telegram from the Kiel Centralstelle 

 announces the discovery ot a new comet by the Rev. J. H. 

 .Metcalf at Taunton, Mass., on .August 9. The position, at 

 9h. i5-2m. (Taunton M.T.), is given as R.A. = i6h. lom., 

 dec. = 15° 20' N., and the comet was said to be moving in 

 a south-westerly direction ; at the time of discovery the 

 brightness of the comet was about equal to that of an 

 eleventh-magnitude star. 



-A later telegram gives the position of the comet as 

 observed by Mr. Burton at Boston on .August 10 ; at 

 I2h. 28-8m. (Boston M.T.) R.A. = i6h. lom. 29-3S., and 

 dec. = 14° 56' 41". The comet is on the meridian at about 

 6h. 30m. p.m. 



Observations of Comets. — Dr. Max Wolf records an 

 observation of comet 1910a, on July 15, in No. 4429 of the 

 Astronomische Nachrichlen (p. 210). The comet was then 

 a little to the south-east of v Cygni, and its photographic 

 magnitude was 16-5. 



In No. 4430 of the same journal he states that on plates 

 taken on April 11 he has found images of comet 19096 

 (Daniel); the comet was then tainter tnan Halley's at tne 

 time of discovery, and was not shown at all on a plate 

 which had a longer exposure on May 12. In compliance 

 with a request from Herr Jan Krassowski for unpublished 

 observations of comet 1909c, Dr. Rambaut also publishes 

 some positions of this comet, secured at the Radcliffe 

 Observatory during December, 1909, and January, 1910. 



Observations of Mercury. — During July and Sep- 

 tember, 1909, observations of Mercury were made at the 

 Revard (.Aix-les-Bains) and the Massegros (Lozfere) 

 observatories by MM. G. and V. P'ournier, and the draw- 

 ings are now reproduced and discussed by M. Jarry- 

 Desloges in the August number of the Bulletin de la 

 Societe astronomique de France. Those made at Masse- 

 gros, with a refractor of 29 cm. (11-5 inches) aperture at 

 an altitude of 900 m-, show that there are definite mark- 

 ings on the surface of the planet which can be seen and 

 delineated by different observers at different times with 

 striking agreement, although the observing difficulties are 

 very great. A dark patch on the southern horn is shown 

 on all the drawings, and in some even obliterates the 

 actual cusp. Other markings agree on different drawings, 

 and can also be identified with some observed by Schia- 

 parelli and Lowell. The observations confirm the state- 

 ments that the rotation period of Mercury is probably 

 equal in length to the planet's revolution period. 



Dispersion of Light in Interstellar Sp.ace. — Recog- 

 nising the importance of the results obtained by MM. 

 Nordmann and Tikhoff regarding the differential velocities 

 of light of different wave-lengths through interstellar 

 space, Herr Beljawsky made a number of observations of 

 the .Algol variable RZ Cassiopeiae during the autumn of 

 1909. Using filters which transmitted either visual rays 



