February 21, 1895] 



NA TURE 



395 



problems which gave rise to the functions, deals with their 

 properties, expansions involving them, semi-convergent expan- 

 sions, Fourier-Bessel expansions, complex theory, definiie 

 integrals, and the relation of the functions to spherical 

 harmonics. The physical apjjlicaiions embrace flow of heal 

 and electricity, vibrations of membranes, hydrodynamics, 

 electrical waves along wires, diffraction, and a number ol 

 miscellaneous problems. Numerical tables are appenaed, and 

 also the Tables of Functions with imaginary argument, which 

 have been prepared by Prof. A. Lodge for the British Associa- 

 tion. A note containing useful formulae for the calculation 

 of the roots of Bessel Functions and others related to them, has 

 been added from a manuscript placed at the disposal of the 

 authors by Prof. J. McMahon. 



We have received Parts iv. and v. of Indian Meteorolo;^ical 

 Memoirs (vol. v.), containing the discussion of hourly observa- 

 tions made at Allahabad and Lucknow, forming a portion of the 

 harmonic analysis of the observations recorded at twenty-five 

 observatories in India, since the year 1S73. The investigation 

 is carried out in a most thorough manner, and there can be no 

 doubt that when the work is complete, and the results correlated, 

 much light will be thrown upon the laws which regulate 

 atmospheric movements in those parts. In any case, the dis- 

 cussion will take rank among-it the most important cfthe kind 

 hitherto undertaken by any country. 



A COMPOUND of grape sugar with one of the acid radicle 

 derivatives of hydrazine recently prepared by Herr Siruve, a 

 pupil of Prof Curtius, is described by Dr. Wolff, of Berlin, in 

 the current Berichte of the German Chemical Society, and, on 

 account of its properties and mode of formation, appears 

 likely to be of considerable service in the commercial extraction 

 of pure dextrose from syrupy mixtures. It is first shown that 

 the sugars of the aldose type react with the acidylhydrazides to 

 produce an aldose-acidylhydrazide by direct addition with 

 elimination of a molecule of water. Thus, in the case of 

 dextrose and benzliydrazide the following equation represents 

 the change : 

 C,H,,.C : O.NH.NH.. -f O : QHi.Os = 



CsHs.C.O.NH.N.CgHioOj ^- H„0. 

 When dextrose and benzh)drazide are digested with 96 per 

 cent, alcohol for five or six hours in a flask provided with 

 an uptight condenser, the new compound is produced in solution 

 in the alcohol, and upon subsequent evaporation it separates in 

 the form of acicular crystals, which can readily be purified by 

 recrystallisation from alcohol. The crystals melt at 171-172' 

 with partial decomposition. As Icevulose does not react with 

 benzhydrazide, pure dextrose can readily be isolated from the 

 mixture of Isevulose and dextrose in ordinary invert sugar by 

 utilising the aliove reaction. The invert sugar is evaporated 

 to a thick syrup, and the latter digested with alcohol and 

 benzhydrazide for about six hours in a reflux still. The alcoholic 

 solution is then evaporated over a steam-bath almost to dryness, 

 the Isevulose is extracted by washing with a minimum of alcohol, 

 and excess of benzhydrazide removed by means of ether. Pure 

 dextrose-benzhydrazide is then obtained in good crystals by two 

 reciystallisations from alcohol. The recovery of dextrose from 

 this compound with benzhydrazide is a very simple matter, for 

 the compound is immediately broken up by boiling water into 

 dextrose and benzhydrazide. It is found convenient in practice, 

 however, to remove one of the products of the dissociation, 

 the benzhydrazide, by precipitation as the insoluble benzal- 

 benzhydrazide by means of benzaldehyde, which is found to be 

 a most valuable reagent for the purpose, .\fter filtration the 

 liquid is evaporated to dryness, dissolved in cold water, whereby 

 any traces of unprecipitated benzal-benzhydrazide are left 

 behind, and again evaporated to dryness. The last | traces 



NO. 1321, VOL. 51] 



of impurities, chiefly benzaldehyde and benzoic acid, are 

 finally removed by dissolving the dextrose in alcohol and pre- 

 cipitating with ether. The dextrose eventually obtained by 

 evaporation of the clear solution is quite pure. Dr. Wolff 

 lastly states that the above is a general process for separating 

 aldoses from mixtures of sugars, and he is experimenting with a 

 view to its adoption on the large scale. 



The additions to the Zoological Society's Gardens during the 



past week include a .Snowy Oivl (Nycfca scandiaca) from 

 Norway, presented by Miss Wright ;' a Dunlin [Trin^a alpitti), 

 British, purchased. 



OUR ASTRONOMICAL COLUMN. 



Mars in 1894. — Si^mr G. Schiaparelli remarks, in No. 3271 

 of the Aslroitomisihe Nachrichten, thitthe unfavourable state of 

 the atmosphere during the o jp jsiti >n of Mars lau yeir ren lerei 

 magnificaiio is beyon 1 230 impossible except in rare instances. 

 Speaking generallv, he says that the "seas" were less pro 

 nounced than in 1S77, and the " canals" were better visible 

 in 1894. and seen in greater numbers. Sjme of the largest 

 ones showed faint traces of dou "ling, but, with the mignifying 

 powers used, nothing coul 1 be male out with certainty on this 

 point. The southern pole ca 1 b 'Came invisible in the i8-inch 

 Milan refractor at the end of October. On October S it had 

 already become very faint. Tfie total disappearance cannot 

 have been later than October 29, i.e. on the 59th day after 

 the southern solstice of the planet. This is unusually eirly. 

 In 1877-78 it was well seen as late as gS days after the solstice. 

 In the present case it is preHy certain that the whole of the 

 southern pole cap was melted. A great change was also 

 observed in the isthmus or peninsula of Hesperia, which 

 separates the Mare Tyrrhenum from the Mare Cimmerium. 

 It was apparently separated into two unequal portions by a 

 newly formed.channel. The Mare Sirenum, which in October, 

 1892, had been separated into two pirts, was in October, 1S94, 

 seen to have resumed its ordinary aspect. But on November 

 21 the sepiration had reappeared. "This fact," says 

 Schiaparelli, " and other analogous ones which I have observed 

 in previous oppositions, lead to 1 he conclusion that the abnormal 

 chang-s in the markings of Mars do not take place by chance 

 and without regularity, but that the same variation may 

 reappear, with t le same aspect, even after a long mterv.al of 

 time. The lorm and extent of such changes is determined by 

 some element which is stable, or at least periodic." 



Novel Methods in Photometry. — The determination of 

 the times of exposure of a photographic plate which are 

 required to produce the same density of film when exposed to 

 ditlerent light sources, forms the basis of the methods recently 

 adopted by Dr. Janssen for inve-tigating the brightnesses of 

 the heavenly bodies (Bull. Mens. Soc. Ast. de France, 

 February). In the case of stars, the plate is placed a little 

 within the principal focus of a telescope; so tnat a disc, or 

 " stellar circle," replaces the almost point-like image ordinarily 

 obtained ; a series of exposures is made on one star, and an- 

 other series on the star to be compared with it : the two images 

 of the same density are thus identified, and the photographic 

 brightnesses of the two stars are inversely as the durations of 

 the corresponding exposures. To compare the light of a star 

 with the sun, an opaque screen, pierced with holes of the same 

 size as the stellar circles, is placed in front of the photographic 

 plate, and these holes admit suni ight to the plate at the moment 

 a triangular aperture in another metal plate is passed over them 

 on releasing a spring ; in this way a series of circles of increas- 

 ing intensity is impressed on the plate, and can be comp.ired 

 directly with the stellar circles. 



In its application to nebulae, Dr. Janssen's method promises 

 to be of great value. On the same plate which has been ex- 

 posed to a nebula, a series of "stellar circles" is formed by 

 directing the instrument to a star in ttie neighbourhood which 

 shows no signs of variability. In the future, when one wishes to 

 obtain a photograph of the nebula which will be strictly com- 

 parable to one taken previously, it will only be necessary by 

 means of stellar circles to determine the exact exposure which 

 should be given. 



From an inquiry into the photographic luminosity of the tail 



