464 



NA rURE 



[March 15, 1894 



its continuation for many years to come. We would, however, 

 suggest that its value for purposes of immediate reference would 

 be greatly enhanced by its publication being more prompt. 



The additions to the Zoological Society's Gardens during 

 the past week include a Wild Cat {Felis catm) from Inverness- 

 shire, presented by Mrs. Ellice ; a Solitary Thrush {Moniicola 

 cya?ms) European, presented by Mr. J. Young ; a Diana 

 Monkey (CercopitJucus diana, var. ignitus, 9 ) from West 

 Africa, deposited ; three Alpine Accentors {Accentor coUaris), 

 a Bluethroat {Cyanecula suecica) European, purchased. 



OUR ASTRONOMICAL COLUMN. 



A New Achromatic Object-glass.— It is well known that 

 in consequence of the irrationality of dispersion the nominally 

 achromatic object-glass is really very far from achromatic. There 

 is always a residual colour, frequently called the secondary 

 spectrum, so that the images of bright stars are surrounded by 

 halos of blue and red light. For this reason a refracting tele- 

 scope designed for visual observations cannot be employed for 

 photography. Many attempts have been made to correct this 

 colour aberration of the achromatic lens, but the plans hitherto 

 suggested have never been practically adopted, owing to 

 difficulties of construction, or to the imperfect durability of the 

 glasses employed. Mr. H. D. Taylor, optical manager to 

 Messrs. T. Cooke and Son'^, has recently taken up the question, 

 and he appears to have come very near to a practical solution 

 of the problem. He has aimed at producing an objective which 

 shall be (i) almost perfectly achromatic ; (2) equally well 

 corrected for photographic purposes as for visual purposes ; (3) 

 capable of practical construction in large sizes ; and (4) of 

 ordinary durability. 



The new object-glass which is to satisfy these conditions 

 is a combination of two positive lenses and one negative lens, 

 each made of a kind of glass possessing different optical 

 properties. The necessary glasses are manufactured by Messrs. 

 Schott and Gen, of Jena, and there is no reason to believe that 

 there will be any difficulty in the production of large discs. The 

 separate lenses are so constructed that the partial dispersions of 

 Iwo of the lenses combined are as nearly as possible equal to 

 those of the third lens when acting singly. It is calculated that 

 with the kinds of glass actually available the greatest departure 

 from focus in the case of a 12-inch object-glass of 15 feet focus 

 would be about o'o6 inches for the H rays, or only ,'f that in 

 an ordinary object-glass of similar dimensions. The curvatures 

 of the len-es are designed to minimise the difficulty of practical 

 construction and testmg, and no Important loss of light is 

 anticipated from the increased thickness of glass which the new 

 object-glass requires. Indeed, it is probable that there will be 

 a considerable gain of light-gathering power from the conver- 

 gence of all the luminous rays to a common focus. (Full 

 particulars are given in the Patent Specification, No. 17,994, 

 1892.) 



Solar Magnetic Influences on Meteorology. — Under 

 this title Prof. H. A. Hazen has published a pamphlet dealing 

 with the supposed existence of electric or magnetic fields in the 

 atmosphere, and the possibility of their accounting for weather 

 phenomena. The subject has for some time been under investi- 

 gation by Prof. F. H. Bigelow, and papers upon it have been 

 published by the United States Weather Bureau, and in several 

 American journals. Prof. Bigelow considers that under certain 

 conditions of ihe sun there would be generated two distinct 

 magnetic fields — -one from the photosphere, and one from the 

 nucleus, the earth being traversed by at least three fields of 

 magnetic force : the lines of permanent magnetism, those 

 from the electro-magnetic or radiant field, and those from 

 the magnetic or coronal field. The radiant field would be 

 favourable to producing warm, dry, high-pressure areas, as 

 seen in the tropical belt, while the magnetic polar field would 

 be favourable to the production of cold, dry, high-pressure 

 areas, such as frequent the storm-belts farther north. It is with 

 the latter influence that we have chiefly to do, in which Prof. 

 Bigelow detected systematic changes recurring in about twenty- 

 seven days. On projecting temperature curves for different 



NO. 1272, VOL. 49] 



parts, according to this magnetic ephemeris, he found inter alia 

 that there is a continual lag in the time at which the maximum 

 and minimum points of the curve reach the stations lying to the 

 eastward, e.g. a minimum point in the curve in the eastern part 

 of the country corresponds to a maximum point in the west, and 

 vice vena. Prof. Hazen puts these theories to various tests, 

 amongst them the passage of hot and cold waves across the 

 United Slates, and he concludes that the outcome of these in- 

 vestigations must be a "bitter disappointment " to those who 

 believe in an all-important influence, aside from heat, from the 

 sun upon our weather changes. He admits that there is un- 

 doubted evidence that some influence does exist, but at present 

 it appears to be masked by terrestrial conditions, which have 

 yet to be studied and eliminated. 



A New Telescope for Greenwich. — The Observatory 

 announces that Sir Henry Thompson has offered the magnificent 

 sum of ;/"5ooo to the nation, through the Astronomer Royal, 

 for the purpose of buying a telescope for Greenwich Observatory. 

 The instrument is to be expressly designed for photographic 

 purposes, and, subject to the acceptance of the offer by the 

 Government, will have an aperture of 26 inches. It will be 

 made from the model of the equatorials used for the photo- 

 graphic chart of the heavens, but with double the dimensions of 

 those telescopes. The guiding telescope will be the lafinch 

 Merz refractor, with a light tube. It is intended to house the 

 new instrument under the Lassell Dome, on the top of the 

 central octagon of the new Physical Observatory, now being 

 built in the south grounds of the Royal Observatory. 



OccuLTATiON OF Spica. — On the morning of Good Friday 

 the bright star Spica will be occultated by the moon. At Green- 

 wich the disappearance takes place at 4.5 a.m. at the position 

 angle 123°, and the star will reappear at 5.13 a.m. at position 

 angle 297^, the angles being read from north in the direction 

 north, east, south, west. The occultation will be visible at places 

 between latitudes 79° north and 16' north, which are not too far 

 from the meridian of Greenwich. The moon will be a little past 

 full at the time. 



New Nebul.t.. — Dr. Max Wolf announces in Astr. Nach. 

 3214, that several new nebulous patches appear upon photo- 

 graphs of the regions lound ;3 and I Cassiopr-ise, taken at the end 

 of last year and the beginning of this, with exposures of about 

 sixteen hours. Three of these spots have the follow ing positions : 



h. m. , 



R.A. ... o 49 o Deck ... 6o'20 

 ,, ...051 '9 ,, ... 6o'5 



■ ■• I 380 „ ... 59-5 



THE MINUTE STRUCTURE OF THE NERVE 

 CENTRES. 



'T'HE Croonian Lecture was delivered by Prof. Ramon y Cajal 

 -*- at the Royal Society on Maich 8. After giving a short his- 

 torical survey of his subject and referring to the work of KiJlliker, 

 His, Van Gehuchten, Waldeyer, Edinger, Von Lenhossek, 

 A. Sala, P. Ramon, and Retzius, Prof. Cajal proceeded to give 

 an account of his own work, and pointed out in what particulars 

 his results differed from those of Camilo Golgi, the originator of 

 the silver impregnation method. Goljii had shown that the 

 protoplasmic expansions of nerve cells terminate by free 

 extremities in the grey matter, that the prolongations of the 

 nerve cells give off in their course through the grey matter very 

 fine ramifying collateral branches, and that two types of cells may 

 be distinguished — a motor type, distinguished by an unbranched 

 axis cylinder, which becomes continuous with a fibre in the 

 white matter, and a sensory type, distinguished by possessing 

 an axis cylinder which on leaving the cell divides so freely that 

 its individuality is lost as it ramifies in the grey matter. With- 

 in the grey substance a network of fibres is formed by the 

 terminal twigs of centripetal nerve fibres, ramifications from the 

 network derived from sensory cells, and collaterals of proto- 

 plasmic piocesses of motor cells. 



Passing onto the results of his own woik. Prof. Cajal showed 

 that axis c) linders, in addition to the protoplasmic prolongations, 

 end by free teiminations in the giey sulstance. He does not 

 admit that there is any sharp functioral difference between the 



