402 



SCIENTIFIC NEWS. 



[Oct. 19, i888. 



would have been referred to palaeozoic periods rather 

 than to recent life. But these thrusts are mere skin 

 wounds compared to what is likely to follow, when we 

 consider how very narrow is the scratch on the ocean 

 bottom that has yet been made by the dredge compared 

 with the enormous area that remains unexplored. 



We are evidently moving in the direction of a general 

 inference that physical conditions, not chronological eras, 

 determine the course of geological evolution, both as 

 regards the ph3'sical constitution of rocks and the fossils 

 they contain. At the recent International ^Geological 

 Congress, Dr. Sterry Hunt stated his belief that the 

 action by which the old granites as well as the basic 

 gneisses were formed "had continued since the most 

 remote period, and was going on at the present day with 

 diminished intensity " (see report, Scientific News, page 

 347); and Dr. Hicks, who followed, though differing 

 with Dr. Hunt on the Wernerian and Plutonic contro- 

 versy, "admitted that rocks of volcanic origin could 

 change at any period of the world's history into crystal- 

 line schists under favourable conditions." It would be 

 difficult to find two higher authorities on this particular 

 part of the subject than these. 



Many who are not experts in geology have been, and 

 still are, deceived by the manner in which the term 

 "carboniferous group " or " strata " is used in geological 

 treatises. They imagine that coal is only found in the 

 " carboniferous strata." As a matter of fact, all the strata 

 of all ages, from the lowest of the palaeozoic to the recent, 

 are more or less carboniferous. The strata which have 

 received the distinctive title of "carboniferous" are 

 simply those which in the British Isles and some other 

 places are specially rich in one particular kind of coal. 

 This kind of coal and other kinds of coal abound in other 

 countries both above and below our coal measures, and 

 even in our country good workable coal is found below 

 this and below the millstone grit (or ". farewell rock," as 

 our local miners call it, from their experience of the 

 hopelessness of finding coal when it is reached). Coal is 

 found and worked in the mountain limestone and lime- 

 slone shales of Durham, Northumberland, and Scotland. 



Returning to the idea of an era of carbonic acid excess 

 in our atmosphere, it should be remembered that even 

 in our " carboniferous group " there is no indication of a 

 general excess of vegetable growth at that period ; the 

 coal seams are partial deposits found here and there in 

 lake basins or long estuary troughs. 



Besides this we must remember that if at that period 

 the whole world were immersed in an atmosphere con- 

 taining any great excess of carbonic acid beyond that now 

 prevailing, all terrestrial animal life would have been 

 destroyed, the chain of evolution broken asunder in such 

 a manner that the course of creation of land animals and 

 birds, if not of the marine vertebrata also, would have 

 to start afresh. This is directly contradicted by the geo- 

 logical record. 



- — *^t^> ( ^3< : -> 



SOME PHOTO-MICROGRAPHIC 

 APPARATUS. 



(Continued from p. 379.J 

 A NOTHER form of apparatus made by Messrs. Swift 

 -**- is shown in the woodcut, fig. 4. In this case the 

 whole apparatus is mounted on a table, which is sup- 

 ported on three legs, which, to add to the portability of 

 the instrument, are made to unscrew. 



The microscope supplied with the apparatus has 



rackwork motion to the internal draw-tube for use in the 

 adjustment of an amplifier, when such is required. A 

 stop is placed across the claw-foot of the microscope, to 

 ensure the tube being brought correctly to the horizontal 

 position. 



A slot traverses nearly the whole length of the top 

 of the table, along which the illuminator apparatus, the 

 board upon which the microscope is fixed, and the camera 

 are made to slide. 



The camera is constructed to take plates up to 6J in. 

 by 4^ in., and has a range of from 6 in. to 30 in., and a 

 double rack-work arrangement for effecting this extension. 



Focussing with the fine adjustment can be done from 

 the back of the camera by means of a rod carried along 

 the side of the table, at the end of which is a pulley, 

 over which a fine cord passes to the milled head of the 

 fine adjustment. 



Specially corrected objectives are supplied for use 

 with this instrument, by the aid of which the object to 

 be photographed can be definitely focussed upon the 

 screen, since the actinic and visual foci are identical. 



With this apparatus excellent work can be done. 



Fig. 5 shows a very perfect apparatus designed by 

 Dr. Crookshank, and made for him by the last-named 

 firm. The instrument was specially designed for use 

 with very high power objectives, for the photography of 

 Bacilli. How excellent are the results obtained, can best 

 be judged by reference to Dr. Crookshank's work, " Photo- 

 graphy of Bacillus," the photo-lithographic illustrations 

 in which were produced from negatives procured by 

 means of this instrument. 



Owing to the small amount of light passing through 

 the lenses of high power objectives, illumination by 

 means of paraffin would necessitate very long exposures ; 

 the oxy-hydrogen limelight is therefore used as the 

 illuminant, a special series of lenses for condensing the 

 light on to the object being arranged in front of the 

 lantern. The heat arising from the condensation of a 

 powerful light on the object under examination would 

 probably injure it by melting the medium in which it 

 is mounted ; to obviate this, a glass trough containing 

 a strong solution of alum is inserted between the con- 

 densing lenses, the action of the alum being to absorb 

 most of the heat rays in the illuminating pencil. 



Fig. 5 shows the apparatus in the position in which 

 it is most generally used, but in case it is desired to 

 photograph liquids, the apparatus can be brought to the 

 vertical position. This is done by removing the two 

 bars which act as ties between the legs which support 

 the instrument, folding the leg at the lantern end of the 

 table beneath the board, and traversing up the back legs 

 by means of the screw provided for the purpose. A slab 

 is provided, which, together with these legs, supports 

 the instrument very securely. 



A few words descriptive of the arrangement of the 

 apparatus may be found of interest. The oxy-hydrogen 

 lantern and the microscope are mounted on a table 

 which rotates on metal centres, thus enabling the micro- 

 scope to be turned to one side for centering, etc. The 

 lantern can be moved to or from the sub-stage, as may 

 be found necessary for the adjustment of the illumina- 

 tion. The camera is very similar to that before described 

 in Swift's apparatus, having a range of 30 in. 



The fine adjustment is done from the back of the 

 camera by means of the usual rod carried along the table, 

 but the arrangement differs considerably from any 

 before described. 



