f 



November 12, 1891] 



NATURE 



47 



Chadwick described the Leach lantern microscope as follows. 

 The microscope can be applied to any oxy-hydrogen lantern. 

 It is screwed on the front in place of the ordinary lantern ob- 

 jective, the size of flange required being 2\ inches ; when the 

 lantern objective flange is larger than this, an adaptor must 

 be provided ; and when the draw-tube of the lantern is 

 "ricketty," a rigid lengthening tube may be adapted. The 

 lantern condenser should be about 4 inches or 4^ inches in 

 diameter, and of the triple form. The stage of the microscope is 

 open at both sides, and at the top also, and serves for all classes 

 of objects, whether ordinary microscopic slides or polariscope 

 crystals, shown with either narrow angle rays or by the convergent 

 system of lenses. The stage being so constructed, it is extremely 

 accessible for the introduction of sub- condensers, with which the 

 instrument is provided. The object-holder is quite a novel idea, the 

 principal mechanism of it is placed under the stage (to be out of 

 the way) ; two arms passing through slots in the bottom of the 

 stage, actuated by a spring and manipulated by a milled head, 

 serve to hold the objects flat against the inside surface of the 

 front of the stage. The diaphragm, or compound wheel of 

 diaphragms, is rotative on a pivot attached to the plate arm in 

 such a manner that the whole may be raised out of the field 

 altogether, and dropped into it again, in an instant ; when the 

 wheel is raised, a spring catch holds it in position. When in 

 this position the whole field of the microscope can be utilized 

 for showing objects up to \\ inches in diameter. When, 

 as in using polarized light, it is desired not to be incom- 

 moded with the diaphragms, the detachable plate carrying the 

 compound wheel can be instantly removed from the stage, and 

 when again required it can be as quickly restored. The arms 

 of the object-holder projecting through the bottom of the stage 

 have sufficient lateral movement to admit any zoophyte trough or 

 wooden frame or combination of wooden frames up to i inch in 

 thickness. Thus the advantages of this arrangement are clearly 

 manifest. The two sub-condensers with which the instrument 

 is provided are found to give satisfaction with all objectives of 

 from 2\ to xV inch focus. When the light has been properly 

 concentrated, high powers can be used. It should also be 

 observed that when high powers are used the front lens of the 

 objective is open to the view of the manipulator, a great con- 

 venience when inserting the object, by enabling it to be imme- 

 diately adjusted within the area of the lens. When polarized light 

 is to be used, the polarizing prism must be pushed into the rotating 

 tube of the instrument by removing the concave lens at the back, 

 and after inserting the prism this concave lens may be replaced 

 in an instant. The rotating tube is an advantage over fixed 

 tubes, as the polarizing prism can by this arrangement be placed 

 in any desired azimuth which best suits the object. The con- 

 vergent system of lenses for use with polarized light in transmit- 

 ting rays through biaxial crystals was worked out by Mr. Leach. 

 It gives powerful illuminations, and includes an angle of 170°. 

 The front focussing arrangement was introduced by Mr. Leach 

 in 1883. Before that time several supplementary lenses had to 

 be kept in readiness for use, as different classes of crystals were 

 placed in the polariscope. Mr. Leach discovered how these 

 supplementary lenses might be dispensed with, and fitted up his 

 system accordingly ; and now all makers of first-class polariscopes 

 attach to their instruments this great improvement. The con- 

 cave field lens, with which the instrument is provided, is abso- 

 lutely necessary when the polarizing prism is in use. With 

 all powers it enlarges the field, and equalizes the distribution of 

 illumination. The three objective adaptors with which the instru- 

 ment is provided admit of any microscope power with the 

 standard screw ; they are made to slide in the front tube of the 

 microscope, which is provided with a rack and pinion, and also 

 with a fine screw movement. Thus, by having the various powers 

 already screwed into the adaptors, one may be changed for 

 another almost instantaneously. And into the front or tube 

 portion of these adaptors the tube of the amplifier is made to 

 slide. The amplifier which is provided is a Barlow lens, and 

 being achromatic, it enhances the aplanatic qualities of the 

 objective. It has been asserted "that high power cannot be 

 used in the lantern microscope ; that it is unable to exhibit fine 

 detail upon the screen, and that no alum trough is required." 

 No doubt this is all true so far as applied to inefficient instru- 

 ments. But the Leach microscope does require an alum trough, 

 because where great light is concentrated from the oxy-hydrogen 

 luminant, great heat must, from the very nature of the means 

 employed, be concentrated with it, and the alum trough is the 

 only practical thing which can be used to absorb the heat rav-=- 



The alum trough is of large size, and is used in the ordinary 

 slide stage of the lantern. At the conclusion of the paper, 

 Messrs. Chadwick and Leach gave a demonstration with common, 

 and polarized light. 



Cambridge. 

 Philosophical Society, October 26.— Prof. G, H. Darwin, 

 President, in the chair. — The officers for the ensuing session 

 were elected as follows :— President : Prof. G. H. Darwin. 

 Vice-Presidents : Prof. Hughes, Prof. Thomson, Mr. J. W. 

 Clark. Treasurer : Mr. R. T. Glazebrook. Secretaries : Mr. 

 J. Larmor, Mr. S. F. Harmer, Mr. E. W. Hobson. New 

 Members of Council : Mr. H. F. Newall, Mr, C. T. Heycock, 

 Mr. A. E. H. Love. — The following communications were 

 made to the Society : — On the absorption of energy by the 

 secondary of a transformer, by Prof. Thomson. — On an experi- 

 ment of Sir Humphry Davy's, by Mr. G. F. C. Searle. Two 

 copper wires are passed up through holes about 5 centimetres 

 apart in the bottom of a flat trough, their ends being level with 

 the surface of the trough. Mercury is then poured into the 

 trough to a depth of about 4 millimetres. On sending a powerful 

 current through the mercury by means of the two wires the 

 mercury in the immediate neighbourhood of the electrodes was 

 elevated into a small cone 2 or 3 millimetres in height. — Some 

 notes on Clark's cells, by Mr. R. T. Glazebrook and Mr. S. 

 Skinner. In addition to the causes of variation indicated by 

 Lord Rayleigh, the authors find that the state of amalgamation 

 of the zinc pole may cause a fall in force if the zinc does not 

 show a bright surface. This is worked out by means of a testing 

 cell into which the faulty zincs are transplanted. The result is^ 

 confirmed by Swinburne's experiments on zinc rods in zinc 

 sulphate solution. To correct this fault previous amalgamation 

 in the presence of dilute sulphuric acid is recommended, or 

 immersion of the zinc in the paste. Dr. Hopkinson's method 

 of testing cells by tapping was shown. — Illustrations of a 

 method of measuring ionic velocities, by Mr. W. C. D.. 

 Whetham. — On gold-tin alloys, by Mr. A. P. Laurie. 



Paris. 



Academy of Sciences, November 2. — M. Duchartre in the 

 chair. — On aberration, by M. Mascart. — Note on Mont Blanc 

 Observatory, by M. J. Janssen. This is a brief report of the 

 attempt to reach the rock through the snow on the summit of 

 Mont Blanc, in order to obtain a foundation for a proposed 

 Observatory. In spite of circumstances which rendered the pro- 

 posed building impossible, M. Janssen believed that an edifice 

 of some kind resting on the snow would permit the necessary 

 observations to be carried on, and had one constructed accord- 

 ing to his ideas. No displacement of the erection occurred 

 during the twenty days previous to M. Janssen's departure from 

 the summit of the mountain. The construction of a similar 

 but more important building is therefore contemplated for next 

 year. — Note by M. Armand Gautier, accompanying the presenta- 

 tion of his work on '* Biological Chemistry." — On the Arago 

 Laboratory, by M. de Lacaze-Duthiers. — Contribution to the 

 natural history of the truffle : parallelism between the Terfaz or 

 Kama ( Terfezia, Tirmania) of Africa and Asia and the truffles 

 of Europe, by M. A. Chatin. In the comparison the points 

 considered are geographical distribution, climate, soil, nutritious 

 plants, periods of ripening, depth in soil, and numerous other 

 characteristics. — An excursion in the Rocky Mountains, by M. 

 Albert Gaudry. At the end of the recent Geological Congress 

 at Washington a party was organized to visit the Rocky Moun- 

 tains. An account is given of some of the objects of geological 

 interest observed by the excursionists. — Note on the storm that 

 visited Martinique on August 18, 1891 (an extract from the 

 American Journal of Meteorology), by M. Faye. — Researches 

 on butylene monobromides, by M. E. Reboul. There are three 

 butylene monobromides known besides the isobutylene of 

 Boutlerow. The author describes the preparation and proper- 

 ties of one of these, to which he assigns the constitution CH3 — 

 CH3— CBrrrCH2. He proposes to term it ethyl-acetylene 

 o- hydrobromide. — Observations of two new asteroids discovered 

 at Nice Observatory on September 24 and October 8, 1891, by 

 M. Charlois. Observations of position are given. — On the 

 dimensions and form of the section of a stream {veine) of gas 

 under limited counter-pressure during a limited delivery, by M. 

 Parenty. — On a model of a luminous fountain, by M. G. 

 Trouve. — On the direct combinations of metals with chlorine 

 and bromine, by MM. Henri Gautier and Georges Charpy. 



NO. II 50, VOL. 45] 



