April 23, 1896] 



NATURE 



599 



^'Angular Measurement of Optic Axial Emergences." By 

 William J. Pope. 



The ordinary methods of determining the angle, a, between 

 the direction of emergence of an optic axis into air and the 

 normal to the crystal plate, being very inaccurate unless the plate 

 has a highly polished surface, the author has devised a new 

 method by which this angle, o, can be determined to within 2 or 

 3 minutes of arc. The crystal is mounted in the Fuess axial angle 

 apparatus, and a reading taken for the air emergence of the optic 

 axis ; a cell containing oil of known refractive index, /t, is 

 then brought up round the crystal plate, and a new reading 

 taken for the oil emergence of the optic axis. From the differ- 

 ence of the two angular readings, a.-Q, the angle a may be 

 calculated from either of the formula 



cot o = cot (a - tf) - l//i sin (o - fl) 

 or 



tan (o + e)/2 =/t + i/a* - I tan (a - fl)/2. 



Series of test measurements are given, proving the efficacy of 

 the method ; when o is 53" 24', and yi is i 6473, the measured 

 value of a-9is 24° 15', a fairly large angle. Oil of the highest 

 attainable index of refraction should be used in order to obtain 

 maximum values of a - ; the refractive indices are conveniently 

 determined by aid of the Pulfrich total-refractometer. 



March 26. — "Additional Report on Erect Trees containing 

 Animal Remains in the Coal Formation of Nova Scotia." By 

 Sir J. William Dawson, F.R.S. 



Linnean Society, April 2.— Mr. J. G. Baker, F.R.S., 

 \'ice-President in the chair. —On behalf of Dr. F. Arnold, of 

 Munich, the Secretary exhibited several photographs of typical 

 lichens, received in continuation of a series which has been for 

 some time past in course of issue by that well-known licheno- 

 1 )gist. — Mr. M F. Woodward exhibited a very young example 

 of the "Spiny Ant-eater," Echidna actileata, taken from the 

 mammary pouch of the parent at Newcastle, Western Australia, 

 by Mr. H. B. Woodward, Curator of the Perth Museum. It 

 was intermediate in size between two stages described by Prof. 

 P.irker, but showed no trace of the calcaneal spur characteristic 

 of the male, nor any trace of the mammary pouch peculiar to 

 the female. He called attention to the flattened and beak-like 

 character of the snout and the vestiges of the " egg-breaker," 

 and to the disposition of the spine papillae. For the purpose of 

 comparison, Mr. Woodward exhibited also the heads of 

 Ornithorhynchiis and Echidna, and a male and female mam. 

 mary foetus of Perameles. — A paper was read by Mr. C. H. 

 Wright, " On the Genus Stemona, Lour.," one of the few mono- 

 cotyledonous genera whose flowers are constructed on a tetra- 

 merous type, and remarkable for the diversity of its vegetative 

 characters, while its floral structure varies between comparatively 

 narrow limits. — Lieut. -Colonel C. T. Bingham, in a paper on 

 some exotic fossorial Hymenoptera in the British Museum (com- 

 municated on his behalf by Mr. W. F. Kirby), enumerated 

 thirty-four species, of which no less than thirty were previously 

 undescribed. The discovery of many of these was due to the 

 researches of the author, who had spent twelve years collecting 

 in Sikkim, Burma, and Tenasserim. — The President then gave 

 a descriptive account of the Khasia Hills from personal experi- 

 ence, dwelling on their geological formation, the extraordinary 

 rainfall of the district (i20 inches in five days), and the chief 

 characteristic features of the flora and fauna. 



Royal Meteorological Society, April 15. — Mr. E. 

 Mawley, President, in the chair. — Mr. W. Ellis, F.R.S. , read 

 :i paper on the mean amount of cloud on each day of the year 

 at the Royal Observatory, Cireenwich, on the average of the 

 fifty years 1841-90, in which he showed that a principal 

 maximum occurs in winter and a principal minimum in autumn, 

 with a secondary much less pronounced maximum in summer 

 and a secondary minimum in spring. There is, however, 

 considerable irregularity in the succession of daily values, the 

 differences between which on consecutive days are in numerous 

 cases relatively large. Cloudless days are most numerous in 

 spring and autumn, and least so in winter and summer ; days of 

 little cloud are somewhat less numerous in winter as compared 

 with other parts of the year, whilst days of medium cloud are 

 much more numerous in summer than in winter. Days of much 

 cloud are nearly equal in amount in all parts of the year ; whilst 

 iivercast days are much more numerous and nearly equal in 



amount in the first and fourth quarters of the year, much less 

 numerous in the second quarter, and again less numerous in the 

 third quarter.— Mr. E. D. Frid lander gave an account of some 

 observations of the amount of dust in the atmosphere made at 

 various places during a voyage round the world in 1894-95. The 

 experiments, which were made with a form of Aitken's pocket 

 dust counter, showed that there are often considerable variations 

 in the number of dust particles in a very short space of time. 

 Not only did dust occur in the air of inhabited countries, over 

 the water surfaces immediately adjoining them, and up to an 

 altitude of 6000 or 7000 feet amongst the Alps, but it was also 

 found in the open ocean, and that so far away from any land as 

 to preclude the possibility of artificial pollution, and its existence 

 has been directly demonstrated at a height of more than 13,000 

 feet. — Major H. E. Rawson gave an analysis of the Greenwich 

 rainfall records from 1879 to 1890, with special reference to 

 the declination of the sun and moon. 



Edinburgh. 

 Royal Society, April 6.— Rev. Prof. Flint in the chair.— A 

 communication by Drs. Stewart and Young, of the Public Health 

 Laboratory, Edinburgh University, on the bacteria in milk as 

 supplied in Edinburgh, and the relative efficiency of different 

 methods for their removal, was read by the former. Since 1894, 

 samples of milk from dairies all over the town had been 

 examined, and it was found that bacteria were most numerous 

 between July and October. The milk from dairies with cow- 

 houses in town contained, five hours after milking, more than 

 eight times the number of micro-organisms in milk from dairies 

 supplied from the country. Methods for sterilising were de- 

 scribed, but each imparted a boiled taste to the milk. Scalding, 

 at 176° F., would keep the milk sterile for twenty-four hours 

 if great care were taken, but when performed on a large scale 

 there could be no guarantee, owing to possible post-scalding con- 

 tamination, that the bacillus of tubercle and diphtheria were not 

 present. — Dr. J. Macintyre, Glasgow, indicated some new re- 

 sults which he had got with the Rontgen X-rays. He described 

 his methods for reducing exposure and obtaining definition, and 

 exhibited photographs of different parts of the skeleton of the 

 living subject. Among these were that of one side of the head, 

 obtained by putting the tube so near the other side that its 

 image was eliminated, the sternum and ribs, and the vertebral 

 column with scapula and clavicle. Dr. Macintyre described 

 screens of different kinds which he had made, of which the one 

 saturated with barium platinocyanide was the best. He suggested 

 the use in surgery of fluorescent screens for the cavities, such as 

 the mouth, throat, and maxillary antrum, and exhibited the result 

 of an attempt at photographing tissue. In the kidney, from a 

 cadaver shown, the distinctive in structure of the different parts, 

 and the presence of a calculus, were quite apparent. — Dr. W. G. 

 Aitchison Robertson read a summary of an investigation regard- 

 ing the digestion of starch in the stomach. He showed under 

 what conditions, normal and abnormal, amylolysis ceases in the 

 stomach, and the effect which the gastric secretion has on the 

 ferment ptyalin. — A communication from Lord Kelvin on 

 impulsive fluid motion was held as read. 



Paris. 

 Academy of Sciences, April 15.— M. A. Cornu in the 

 chair.— On fallow ground, by M, P. P. Deh^rain. The ancient 

 practice of allowing land to lie a year fallow after three years 

 cultivation is shown to have rested upon a sound basis, the land 

 increasing considerably in nitric nitrogen during the fallow year. 

 With modern manures the necessity for this no longer exists, 

 although the practice still survives in many parts of Europe. — 

 Nitrates in spring water, by M. T. Schloesing.— On a letter 

 from Gauss, of date June 16, 1805, by M. de Jonquieres. The 

 letter was written to M. Delisle, Professor of Mathematics at 

 Orleans. — On the products of combustion of an acetylene burner. 

 Explosive mixtures of acetylene and air, by M. N. Grehant. 

 The combustion of acetylene in an ordinary fish-tail burner is 

 complete, the products not comprising the least trace of a com- 

 bustible gas containing carbon. With mixtures of acetylene 

 and. air the most violent explosion was produced when the 

 volume of air was nine times that of the acetylene. — On certain 

 classes of Laplacian equations with equal invariants, by M. A. 

 Thybaut.— Verification of Kerr's law in absolute measure, by 

 M. Jules Lemoine. By the use of a condenser having carbon 

 disulphide as the dielectric, with potentials varying from 5000 



NO. 1382, VOL. 53I 



