yan, 23, 1890] 



NATURE 



287 



soil free of nitrogen have added to it a small quantity of soil- 

 extract containing the organisms, the plants will fix much more 

 nitrogen than was otherwise available to them in the combined 

 form. It further seemed probable that the growth and crop 

 residue of certain plants favoured the development and action of 

 special organisms. It is admittedly not yet understood, either 

 in what way the lower organisms affect the combination, or in 

 what way the higher plants avail themselves of the nitrogen thus 

 brought into combination. . , . Should it be firmly established 

 that such an action does take place in the case of certain plants, 

 though not in that of others, it is obvious that part, at any rate, 

 of the gain of nitrogen by the soil supporting the mixed herbage 

 of grass land may be due to the free nitrogen of the air brought 

 into combination under the influence of the action supposed," 

 This must be regarded as an important concession to the view 

 that nitrogen may be derived for the purposes of plant nutrition 

 from the inexhaustible ocean of the atmosphere, and it will 

 probably not be long before the vexed question of the sources of 

 nitrogen in soils will be placed upon a more satisfactory basis. 



John Wrightson. 



SOCIETIES AND ACADEMIES. 

 London. 



Royal Society, December 5, 1889. — "A New Form of 

 Wedge Photometer." By Edmund J. Spitta. 



The author explained that his attention was called to the 

 necessity of devising an arrangement of this nature during a 

 series of experiments upon which he has for some time been en- 

 gaged to ascertain the cause or causes of the discrepancy pre- 

 viously shown to exist when points of light are photometrically 

 compared with objects of sensible size (" On the Appearances 

 presented by the Satellites of Jupiter during Transit," Monthly 

 Notices R.A.S., vol. 48). This investigation has served to 

 indicate that a portion of the error to which reference has been 

 made arises from the wedge form itself when employed upon a 

 disk of any appreciable area, for it will be remembered that 

 hitherto this instrument has only been employed upon points of 

 light such as is exhibited by the stars. Woodcuts are given to 

 explain how this takes place, but it may be briefly stated, that as 

 the field of view in a single wedge photometer is of necessity 

 variable in intensity of absorption, so the preceding limb of a 

 disk is not extinguished at the same part of the wedge, and so 

 not at the same "wedge-reading," as i\ie folloivittg limb. Hence 

 when comparing two different sized disks it is not difficult to 

 understand that an error in the " wedge-interval," technically so 

 called, must inevitably occur. To meet this difficulty, the error 

 resulting from which will of necessity vary with the size of the 

 area under consideration, the new photometer has been devised. 



It essentially consists of two wedges of neutral tinted glass, 

 arranged to pass one another in equal proportions by the turning 

 of a single milled headed screw. A little consideration suffices 

 to show that by this exceedingly simple means, the field of view 

 in the photometer must be absolutely uniform in density through- 

 out its extent, but that its power of absorption can be increased 

 or diminished by the shifting of the wedges in the manner de- 

 scribed. Another improvement is submitted by the addition of 

 a wheel of tinted glasses of varying density, which, by revolving 

 in front of the eye-piece, enables the operator to employ the 

 photometer upon objects having a wide range of intensity. The 

 instrument in its complete form, is mounted on the occulting eye- 

 piece {Monthly N'otices J?.A.S., vol. 45) to afford the observer 

 a means of hiding any object or objects not under examination 

 for the time being, which it is needless to point out is a matter 

 of great consideration in all photometric comparisons. 



Mathematical Society, January 9. — ^J. J. Walker, F.R.S., 

 President, in the chair. — The following communications were 

 made : — On the deformation of an elastic shell, by Prof. H.Lamb, 

 F. R. S. — On the relation between the logical theory of classes and 

 the geometrical theory of points, by A. B. Kempe, F.R.S. — On 

 the correlation of two spaces, each of three dimensions, by Dr. 

 Hirst. — On the simultaneous reduction of the ternary quadric 

 and cubic to the forms Ax"^ + By^ + Cz' 4- Bzv", ax^ +/>y^ + 

 cz' + d-u>\ by the President (Sir J. Cockle, F.R.S., Vice- 

 President, in the chair). 



Paris. 



Academy of Sciences, January 13.— M. Hermite in the 

 chair. — On some new fluorescent materials, by M. Lecoq de Bois- 



baudran. In continuation of his recent communication the author 

 has investigated zircon and Zfi ; tin dioxide and samaria ; tan- 

 talum pentoxide and samaria ; tin dioxide and Za ; tantalum 

 pentoxide and Zo ; tin dioxide and Z& ; tantalum pentoxide and 

 Zj3. All these fluorescent substances are fresh examples of the 

 number of spectra obtained from the same active material with 

 different solid solvents. In combination with the agents the sol- 

 vents must naturally always modify the wave-lengths of the bands 

 as well as their constitution, while still leaving to the various 

 spectra of the agents a family likeness, whereby their common 

 origin may at once be recognized. But if the identity or diversity 

 of two active materials has to be determined dy exact wave-length 

 measuretjients, then it becomes essential to operate with abso- 

 lutely similar solid solvents. — Multiple resonances of M. Hertz's 

 electric undulations, by MM. Edouard Sarasin and Lucien de la 

 Rive. Certain experiments are here described, which tend to 

 throw doubt on Hertz's well-known hypothesis on the undulatory 

 propagation of electric induction. The reading of the paper was 

 followed by some remarks by M. Comu, who pointed out that 

 it would now be necessary to receive with the greatest reserve 

 the theoretical consequences drawn by M. Plertz from his re 

 markable researches, more especially as regards the measure- 

 ment of the velocity with which the induction is propagated in a 

 rectilinear conductor. His experimental method will have to 

 be subjected to much careful study before it can be accepted as a 

 demonstration of the identity of light and electricity. — On the 

 relation between the electric and thermal conductivities of the 

 metals, by M. Alphonse Berget. In a previous paper the author 

 described an easy method for measuring, by means of simple 

 determinations of temperature, the thermal conductivity of the 

 different metals relative to that of mercury, whose absolute 

 value had already been determined. He has now extended these 

 determinations to copper, zinc, iron, tin, lead, and several other 

 metals. The tabulated results show that the order of the con- 

 ductivities is the same for heat and electricity, but that the 

 relation of the mean coefficients of thermal and electric conduc- 

 tivity is not absolutely constant. Hence the law of their pro- 

 portionality is only approximately correct, and subject to some- 

 what the same conditions as Dulong and Petit's law of specific 

 heats. — Heat of formation of platinum tetrachloride, by M. 

 L. Pigeon. A process is described for obtaining this substance 

 in considerable quantities, and the heat of formation of the 

 anhydrous chloride is determined at + 20*5 calories. To com- 

 plete its thermochemical study M. Pigeon is now endeavouring 

 to determine its heat of solution in water and that of its hydrate. 

 — On the combinations of gaseous phosphoretted hydrogen 

 with boron and silicium fluorides, by M. Besson. The boron 

 compound has the formula 2BF;j.PH3, and is decomposed by 

 water with liberation of gaseous phosphoretted hydrogen. The 

 silicon compound was obtained in the form of small and very 

 bright white crystals, their composition corresponding to two 

 volumes of phosphoretted hydrogen gas to three of silicon fluoride 

 or thereabouts. These and some other compounds that remain 

 to be studied render the analogy between phosphoretted hydro- 

 gen gas and ammonia still closer. — On the state of equili- 

 brium of a solution of a gas in a liquid, different portions of 

 which are kept at different temperatures, by M. P. Van Berchem. 

 These researches were made with hydrochloric acid and am- 

 monia, their high coefficient of solubility facilitating the detection 

 of slight differences of concentration. The results show that 

 there exists a special state of equilibrium for solutions of gases if 

 the lower part of the solution is cooled, and the upper part heated. 

 — Note on the rotatory power of matezite and matezo-dambose, 

 by M. Aime Girard. Some numerical errors in the author's former 

 papers on the rotatory power of these bodies {Comptes rendus, 

 Ixxvii. p. 995) are here rectified, and the author's fresh experi- 

 ments confirm his previous conclusion that their rotatory power is 

 absolutely identical. — Papers were submitted by M. Emile Picard, 

 on the employment of successive approximations in the study of 

 certain equations with partial derivatives ; by MM. Maquenne 

 and Ch. Tanret, on a new inosite ("racemo-inosite") ; by M. 

 Edouard Heckel, on the utilization and transformations of some 

 alkaloids present in corn during germination ; by M. A. Giard, 

 on the relationship of the annelids and mollusks ; by M. Leon 

 Vaillant, on the bichique {Gobius and Sicydium) fisheries in the 

 island of Reunion ; by M. A. Vaissiere, on Prosopistoma 

 variegatum of Madagascar ; and by M. Salomon Reinach, on the 

 volcanic eruptions supposed to have taken place in France during 

 the fifth century a. d. 



