330 



NATURE 



[February i, 1900 



information on fixing, hardening, imbedding, sectioning and 

 staining, also on selecting diatoms, in the chapters on " mount- 

 ing " now at the end of the book. The number of pages has 

 been increased from 132 to 186. 



A NEW method of attacking the problem of determining the 

 degree of ionisation of complex solutions is given by Prof. J. 

 G. Macgregor in the Transactions of the Nova Scotian In- 

 stitute of Science just issued. The number of free ions per unit 

 volume can be studied in the case of the two simple salts sepa- 

 rately by means of the conductivity. These numbers are 

 functions of the dilution, and can be expressed graphically in 

 the form of curves. From these two curves, by a neat graphical 

 construction. Prof. Macgregor deduces the concentration of the 

 ions in the solution resulting from the mixture of the two simple 

 solutions, a complicated algebraical process being thus avoided. 

 The method is applied, in a subsequent paper in the«same volume 

 by Mr. J. Barnes, to solutions containing a common positive 

 ion, potassium chloride and sulphate. It was found to be 

 possible in this way, given the dissociation theory and data 

 obtainable from simple solutions, to predict the electrical con- 

 ductivity, specific gravity and surface tension of fairly dilute 

 solutions of potassium chloride and potassium sulphate within 

 the limits of experimental error. 



Nothing can be more striking testimony to the advance of 

 physical chemistry than the manner in which isolated phe- 

 nomena, long known but previously unexplained, fall into line 

 when attacked by modern methods. An excellent example of 

 this is afforded by the paper of Messrs. Cohen and Van Eijk in 

 the current number of the Zeitschiift fiir physikalische Chemie 

 on physico-chemical studies of tin. As early as 1851 a curious 

 molecular transformation of some tin organ pipes was noticed by 

 Erdmann, and the same fact was rediscovered eighteen years 

 later by Fritzsche at St. Petersburg, the tin crumbling to a grey 

 powder. Since that time this phenomenon has been repeatedly 

 studied by various observers, the causes being variously ascribed 

 to low temperature, eff'ect of shocks upon the crystalline struc- 

 ture, and velocity of cooling of the tin when originally cast. A 

 preliminary dilatometric study of a grey tin showed the existence 

 of a transition temperature at about 30° C, hence a transition 

 element was constructed, having grey tin as one electrode and 

 ordinary white tin as the other. A study of the electromotive 

 force of this cell with varying temperatures showed that the 

 reaction 



grey tin 4^ white tin 

 was a reversible one with a transition point at 20° C. A 

 careful determination of the same point by the dilatometric 

 method gave the same value. All the observations of early 

 workers are brought into line by this work. The authors point 

 out that, except during a few warm days, all tin is in a 

 metastabile equilibrium, and tends to transform itself slowly 

 into the grey powder modification. 



The additions to the Zoological Society's Gardens during the 

 past week include a Geoff"roy's Cat {Felis geoffroii) from 

 Paraguay, presented by Mr. W. A. Gillett ; a Woodcock 

 (Scolopax rusticula), British, presented by Mr. C. E. Lambert ; 

 a Common Snake ( Tropidonotus nat7-ix), British ; a Tesselated 

 Snake ( Tropidonotus tcssellalus), a Dark Green Snake {Zaniems 

 gemonensis), European, presented by Miss Ash ; a Black, 

 headed Lemur {Lemur brunneus) from Madagascar, a Blue- 

 tongued Lizard ( Tiliqua scincoides) from Moluccas, a Bare-eyed 

 Cockatoo {Cacatna gyvinopis) from South Australia, two Undu- 

 lated Grass Parrakeets {Melopsiltacus undulatus, var. ) from 

 Australia, two Common Teguexins (Tupinambis teguexin) 

 from South America, an Eyed Lizard {Lacerta ocellata), 

 European, deposited ; a Black- headed Bunting (Eniberiza 

 melanocepha/a), bred in the Gardens. 



NO. 1579, VOL. 61] 



OUR ASTRONOMICAL COLUMN. 



ASTRONOMICAI, OCCURRENCES IN FEBRUARY. 



February 2. 6h. 56m. to 7h. 43m. Occultation of k Piscium 

 (mag. 5-0) by the moon. 

 2. iih. 44m. Minimum of Algol (^8 Persei). 

 2. iSh. 5ni. Transit (Ingress) of Jupiter's Sat. III. 



5. 8h. 33m. Minimum of Algol (0 Persei). 



6. 8h. 36m. to 9h. 24m. Occultation of 8 Arietis 



(mag. 4-5) by the moon. 



7. I4h. 3m. to I4h. 49m. Occultation of 56 Tauri 



(mag. 5-4) by the moon. 



8. I5h. 50m. to i6h. 29m. Occultation of n Tauri 



(mag. 5-2) by the moon. 



14. Venus. Illuminated portion of disc = o*8oi. 



15. I3h. 20m. to I4h. 4Qm. Occultation of 55 Leonis 

 (mag. 6"o) by the moon. 



Saturn. Outer minor axis of outer ring= l6"'l3. 

 i6h. Jupiter in conjunction with moon. % 1° 31' N. 

 loh. 15m. Minimum of Algol (3 Persei). 

 7h. 4m. Minimum of Algol (yS Persei). 



19- 



25- 

 28. 



UNITED STATES NAVAL OBSERVATORY. 

 r'APTAIN C. H. DAVIS, Superintendent of the United 

 ^^ States Naval Observatory at Washington, has forwarded a 

 copy of his report for the fiscal year ending June 30, 1899. 



The great equatorial, 26 inches aperture, has been devoted 

 to work beyond the reach of smaller instruments, and in 

 particular to the spectroscopic determination of the motions of 

 stars in the line of sight. Many measures were made of the 

 diameters of Mercury and Venus, to determine the irradiation 

 error, and it was established that this was a function of the 

 magnifying power employed. 



The spectroscopic observations were almost all made by the 

 photographic method, the wave-lengths being obtained from 

 measures taken with the large Harkness comparator made for 

 eclipse reduction in 1869. The proVjable error in the velocity, 

 as determined from a single plate, was about ± 071 mile per 

 second. Good plates with well exposed comparison spectra 

 have been obtained of o Tauri, o Aurigpe, a Canis Majoris, a 

 Canis Minoris, o Cygni and e Cygni, but many others have 

 been failures, owing to the difficulties involved in the use of a 

 lens only visually corrected. This has recently been remedied 

 by the purchase of a correcting lens of 2-09 inches aperture, 

 which alters the minimum focus from A. 5270 to A. 4341 without 

 materi.ally disturbing the total focal length from the object-glass. 

 Extensive alterations have been made in the endeavour to 

 remedy the air currents produced in the equatorial building on 

 account of its connection with other rooms. The 12-inch 

 equatorial has been employed in the systematic observation of 

 minor planets, comets, occultations of stars and eclipses of 

 Jupiter's satellites, the whole of which have been reduced and 

 published. This telescope has also been used for the exhibition 

 of celestial objects to the public on Thursday evenings. Includ- 

 ing those admitted during day working hours, the number of 

 visitors during the year has been 1623. 



Transit observations have been continuously made through- 

 out the year. The 9'i4 inch instrument was dismounted on 

 June 5, 1899, the whole observing staff" being immediately 

 transferred to the new 6-inch transit circle. The temporary 

 fittings supplied at the installation of the 9*i4-inch transit in 

 1893 ^''^ being replaced by permanent ones of new design. A 

 meridian mark has been provided for the 6-inch instrument, 

 and the performance of both this and the new steel altazimuth 

 have given every satisfaction. 



The new 5-inch altazimuth and the prime vertical instrument 

 have been employed for determining variations of latitude and 

 the constants of aberration and nutation. 



The 40-foot photoheliograph was installed, for obtaining sun 

 pictures, on October 11, 1898, and from this date to June 30, 

 1899, negatives were taken on 122 days. The sun's disc on 

 these plates is 4-3 inches in diameter. The publications of the 

 Observatory are well in hand. Volumes of observations for 

 1 89 1 and 1892 are almost ready for distribution, and these will 

 complete the record of work done at the old Naval Observatory. 

 The American ephemeris for 1902 is issued, and it is hoped 

 that the volume for 1903 will be issued in February 1900. In 

 this, the adopted value of the apparent diameter of the sun will 



