37§ 



SCIENTIFIC NEWS. 



[Oct. 12, Ij 



back doors, and supply themselves, at cost price, by 

 purely domestic arrangements of main pipe and 

 branches. To cover uncertainties, the charge per 1,000 

 cubic feet should be a little above cost, and the surplus 

 divided, pro rata of consumption, in the form of bonus, 

 as is done by the Northern Co-operative Societies. 



There now exists in London some very convenient 

 nuclei for initiating this reform. I refer to the blocks of 

 tall houses that are divided into flats, such as those near 

 1o the Palace of Westminster, on the site of old Oxford 

 Market, in the Marylebone Road, and other places. 

 They are compact, and usually under single proprietor- 

 ship. Surely the enterprising proprietors of some of 

 these blocks might be persuaded to pioneer that most 

 desirable innovation. The fact that the tenants are 

 emancipated from the vulgar cockney prejudice against 

 Hits proves that there are reasoning beings that are not 

 afraid of domestic innovations. 



The five years' work at the Gloucester Asylum, de- 

 cribed in Mr. Dowson's paper, is a step in the direction of 

 domestic gas heating. The cost of 8d. for an equivalent 

 of 1,000 feet of ordinary gas settles the economic ques- 

 tion, for if we could be supplied at one shilling, nothing 

 but dogged stupidity could prevent the general domestic 

 use of gaseous fuel. 



In reference to this subject it is desirable to brush 

 aside the old water-gas fallacy, which still lingers in the 

 mind of some. Water being composed of hydrogen and 

 oxygen, which may be dissociated by heat, and these 

 gases when separated being addicted to such energetic 

 combustion on re-uniting, it has been supposed that we 

 can create abundant calorific energy by the simple 

 dissociation of water, and re-uniting its elements. If 

 such were the case as supposed, the doctrine of the con- 

 servation of energy would be a great mistake. But the 

 fact is, that the work of dissociating water by heat 

 demands precisely the same amount of heat as is given 

 out by the reunion of its elements. The case is strictly 

 analogous to the evaporation of water, and the reconden- 

 sation of the steam. Neither must it be supposed that 

 in passing steam over heated coke or anthracite, and thus 

 obtaining a mixture of carbonic oxide and hydrogen, or 

 in passing air over the same, and thereby obtaining a 

 mixture of combustible carbonic oxide and nitrogen, 

 we create any heat beyond that which is due to the 

 combustion of the fuel that is used for the production of 

 the gas. We actually obtain less by the final combustion 

 of the gas, because some is inevitably lost by radiation 

 and convection in the gas-making apparatus. The 

 advantage consists in the exchange of gaseous for solid 

 fuel, in obtaining cur fuel in a form that is so much 

 more manageable, that can be utilised exactly when and 

 where it is wanted in quantities admitting of practically 

 exact regulation, and with little or no labour, and no 

 dirt. 



In an ordinary open coal fire, from eight to nine tenths 

 of the heat goes up the chimney to warm the clouds. 

 With a gas fire the proportions are reversed, eight to 

 nine tenths are used effectively as required, and only one 

 or two tenths are lost. 



Photographing a Rainbow. — Professor H. Kayser, 

 of Hanover (Naturwissenschaftliche Wochenschrift), has 

 succeeded in photographing a rainbow from the Rigi- 

 Kulm. He took special precautions, and used dry plate 

 coloured with azaline. 



SOME PHOTO-MICROGRAPHIC 

 APPARATUS. 



(Continued from p. 362. ) 



T N cases where an uncorrected objective is used, after 

 obtaining the sharpest possible visual focus, the back 

 of the camera must be racked into the position at which it 

 has been determined the actinic focus lies. 



When very great accuracy of focus is required, it is 

 best to use, as a focussing screen, a piece of plain glass 

 slightly greased by rubbing it upon the hand, and an 

 adjustable focussing glass, set to focus the ground or 

 greased surface of the screen. Through this the grease 

 globules will be readily seen, together with the image of 

 the object falling on the surface of the glass; and as both 

 lie on the same plane, accuracy and sharpness may be 

 relied upon. 



It now remains to substitute the sensitised plate for 

 the focussing screen, and to expose it. 



The exposure must of necessity be long, varying 

 according to th^ colour of the object, the amplification, 

 the volume of light passing through the objective, and 

 the class of plate used. A long exposure is desirable, 

 and with this view, use a medium stop in front of the 

 objective. 



The actual exposure is most readily made by drawing 

 out the shutter of the dark-slide, and when it is judged 

 to be sufficient closing it in again. Some people effect the 

 exposure by placing a small cap over the objective, 

 others by placing a piece of card in front of it, and 

 removing and replacing this for the exposure ; but in the 

 writer's experience the gradual draw ing out of the shutter 

 of the slide does not cause any disadvantage, whilst it is 

 certainly the handiest and safest method. The removal 

 of the cap or card always leaves a chance of interfering 

 with the object on the stage of the microscope. Any 

 light other than that given by the lamp should be pre- 

 vented from entering the objective. - A piece of velvet 

 carefully placed over the stage and tube of the micro- 

 scope will prevent this. 



Such is the apparatus which can be most readily pre- 

 pared, and the necessaries for which are to be found in 

 most households nowadays. 



Specially designed apparatus for the purposes of 

 photomicrography are to be bought, and it may be use- 

 ful to examine their structure. 



In fig. 2 is shown a simple form of photo-micrographic 

 camera designed by Messrs. Watson an.l Sons, of High 

 Holborn, which can be used with any microscope, all 

 that is necessary in this case being some packing 

 beneath the frame on which the camera slides, in 

 order that the axis of the camera and the optical axis of 

 the microscope when in a horizontal position may coincide. 

 A base-board, which is detachable, extends to a 

 sufficient distance in front of the camera to admit of a 

 large microscope and lamp, with ample range for the 

 adjustment of the illumination. The microscope and 

 lamp are fitted on to a board which rotates on the top 

 of the base-board on suitable metal centres, thus enabling 

 the operator to turn the microscope and illuminating 

 appaiatus free from the camera, and into such a position 

 as he may find best suits his convenience for examining 

 and centering the object, with the assistance of an 

 ordinary eye-piece. The rotating table is fitted with a 

 lock which comes into action when the microscope is 

 moved back into its central position, this ensuring 

 accuracy of position on its return. 



