Feb., 1904] . 



KNOWLEDGE & SCIENTIFIC NEWS. 



object as seen through the microscope by such an observer. 

 In making calculations connected with focal lengths 



the most useful formula is ' + , = ^ where p and p' 



p p' f 



denote the conjugate foci, and f the principal focus. 

 When we know the size of the image and its magnifica- 

 tion, and one of the two foci, such as 10 inches, we can 

 use the proportion D :</:;/)' ;/', where D is the diameter 

 of the image, (/ of the object, and />' the longer of the 

 two foci, then, from the equation given above, i.e., 



I 



P 

 I 



P^ 



+ 



P" 

 D + 



f 



and the ratio 



D 

 d 



P' 

 P 



we obtain 



f 



, or more simplj' f = p' 



D + d' 



New Spectrometer Ta.ble. 



Messrs. W. G. Pyc and Cd., of Cambritlge, have re- 

 cently brought to my notice a new combination spectro- 

 meter, the adjustments of which present quite new 

 features, and which might, I think, be adapted to certain 

 microscopic accessories. All motions and fittings 

 are arranged geometrically. The base consists of 

 a heavy iron casting on three levelling screws, having 



a true lathe-turned surface, with two annular V-groo\es 

 in it, one near the outer edge, the other a few inches from 

 the centre. The telescope and collimator are provided 

 with tables or carriages consisting of two pieces each, 

 the lower part having two steel balls and one levelling 

 screw for the feet. The balls work in the larger of the 

 two annular grooves mentioned above, and tiie levelling 

 screw on the plane surface a few inches from the centre. 



The upper part consists of a cr.idle having two V sup- 

 ports in which the telescope or collimator, as the case 

 may be, lies evenly, being held in position by a spiral 

 spring trap. This cradle being clamped by a thumb- 

 screw to the lower part provides the necessary adjust- 

 ment for getting the telescope and collimator into hori- 

 zontal alignment. The V-fittings admit of almost any 

 telescope and collimator being used. The two parts ol 

 the carriage are worked up mechanically true, so that 

 very little adjustment is needed to set them optically 



true after the base has been levelled, which can be done 

 by using a spirit level in the usual manner. 'l"he 

 carriage for the telescope is providetl with a vernier, 

 whilst the one for the collimator has an index pointer 

 only. The prism-plate consists of two parts, the Upper of 

 which is capable of adjustment in the horizontal plane 

 without alTecting the lower part, which has thrcu; 

 spherical ended feet, two resting in the inner V-groove, 

 the other working on the plane surface. The simplicity 

 of the arrangement, and the easy way in which it can be 

 worked up mechanically, combined with its steadiness 

 and large bearing surfaces struck me favourably, and as 

 the arrangement could easily he adapted to a reading 

 telescope, to say nothing of adaptations to a model theo- 

 dolite and se-xtant, circular vernier, simple dividing engine, 

 iSrc. 1 trust its description will not seem out of place 

 here. This instrument, when shown at the Royal Insti- 

 tution on .\pril 3rd last, drew, I understand, considerable 

 attention. 



Recent Patents. 



• 9.750. Natural history specimens, preserving. ^[AT^.•• 

 soviTS, v., Liptoujvar, Hungary. Sept. 9. 

 Beetles are preserved in a manner which keeps the joints flexible 

 by treatment with a lliiid consisting of specified proportions of 

 alcohol, salicylic acid, sal-ammonia, and distilled water, to which 

 arsenic or other substances may be added. The quantity of ammonia 

 to be added depends on the colour of the beetle to be preserved. 

 When thorouglily impregnated, they are placed in a cool closed 

 chamber, to dry, the joints being bent from time to time while the 

 beetles are being dried. The liquid may also be employed in pre- 

 serving diptera, rhynchola, &c 



19,804. Hydrocyanic acid and cyanides. Wolterkck, II. 



C, 3, Edinburgh Mansions, Ilowick Place, Victoria Street, 



London Sept. 10. 



A gaseous mixture of, preferably, equal parts of ammonia, a 



carbon compound, and hydrogen is passed over a suitable catalytic 



agent, such as platinized pumice, strongly heated and coiitaine<l in 



a reaction chamber or series of chambers. The hydrocyanic acid 



may be collected, or it may be absorbed in caustic potash or soda 



to produce a cyanide. The carbon compound may be carbonic 



oxide or acid, or benzene, acetylene, ethyl or methyl alcohol, &c. 



Water gas may be employed for supplying a mixture of carbonic 



oxide and hydrogen. The gases or vapours should be free from 



water. The I'rovisional Specification states that freshly-reduced 



iron may form the catalytic agent. 



19,823. Turbines or impact=wheels. M.»lcArthur, C, 

 and Smith, 1'., both of 75, Church Koad, Woolston, near 

 Southampton, Hampshire. Sept. 10. 



Relates to impact- 

 wheels driven by ex- 

 pansible fluid i)res- 

 sure, and suitable for 

 propelling ships. The 

 impact - wheel has 

 vanes u sloping in op- 

 posite directions alter- 

 nately and of a cor- 

 rugateil or other 

 curv'cd cross-section. 

 The fluid pressure is 

 admitted twice during 

 each revolution by 

 means of a three- 

 ported tubular valve «, 

 which is rocked by an 

 eccentric n on the main 

 shaft III- The admis- 

 sion \-alve is sur- 

 rounded by a ported 

 sleeve h, which forms 

 a reversing- valve, and 

 which can be rocked 

 by a handle /' to admit 

 the fluid to the porty' 

 for forward running or 

 to the port / for back- 

 ward running. Expansion chambers ( are formed in the wall of the 

 cylinder x. 



