422 



NA TURE 



\Scpt. 13, 1877 



in working order. After having fixed in its support the 

 lube filled with mercury, and being assured that the fine 

 extremity dips well into the cup <■', we place the balance 

 in equilibrium by abiding weights to the other scale. The 

 bell-glass v, which has been raised for this operation, is 

 then put in its place, and the instrument is ready for 

 action. 



The registering apparatus is composed of the double 

 differential wheelwork of M. Kddier, which works as fol- 

 lows : — Two wheels m and M' moving in opposite direc- 

 tions, are terminated by small flies, very delicate, and 

 turning very swifily ; they arc connected by a difierential 

 train, the axis of which carries a pulley with a double 

 groove A. Between the two flies oscillates a needle, one 

 extremity of which serves to arrest alternately one of the 

 two flies. At the other extremity a, of the needle, is a 

 soft-iron pallet on which acts an electro-magnet E, every 

 time contact is made by the balance at C. The needle is 

 mounted on an axis which permits it to oscillate right 

 or left according as it obeys the electro-magnet or a small 

 antagonistic spring. 



The double-grooved pulley A carries two threads the 

 one attached to the pencil K and terminating in a weight 

 O, the other bearing a small cylinder and plunging into 

 the cup G containing glycerine and connected by a tube 

 with the cupij placed on one of the scales of the balance. 

 Of course the cups G and g must be placed in the same 

 horizontal plane. A cylinder H, moved by the clock- 

 work L, carries the paper. A second pencil K' serves to 

 trace upon the paper a small mark intended to control the 

 progress of the wheel- work L. This mark may be made 

 automatically by an electric contact proceeding from a 

 regulator of precision. 



Let us see now how things work. Suppose the tempe- 

 rature rises (the explanation which follows will account for 

 the mode of action of the apparatus when the temperature 

 falls), the weight of the mercury in the cup at g' will in- 

 crease, the equilibrium will be destroyed, and the contact C 

 of the balance will be established ; the electro-magnet E 

 will attract the end a of the needle, and the fly of the 

 wheel w' will be free ; the pulley a w'U then turn to the 

 left, the float will sink in the cup G, and the pencil will be 

 directed towards k'. The float of the cup G, in descending, 

 will raise the level of the liquid at G, and at g, and con- 

 sequently will increase the weight in the scale of the 

 balance which holds the cup _;,', and at the moment that 

 equflibrium is thus again established, the contact at C 

 will be broken. The end a of the needle ceasing to be 

 attracted by the electro-magnet will respond to the appeal 

 of the antagonistic spring, and disengage the other fly. 

 This fly of the second wheel M disengaged, permits the 

 pulley A to turn to the right, drawing the pencil from K.' 

 to K, and causing the float of the cup g to reascend, and 

 consequently diminishing the weight at g. That loss of 

 weight breaks anew the equilibrium of the balance, the 

 contact at c is re-established, and the same course is 

 repeated as we have explained above. 



It will be seen from what we have said that the clock- 

 work is always in motion — now to the right, now to the 

 left — even when the temperature does not vary ; the 

 curve obtained has then the aspect of a small zigzag, but 

 so fine that it is difficult to detect it. This arrangement 

 permits, so to speak, the double wheel m m' to test the 

 balance for the slightest change in the conditions of 

 equilibrium. 



The tube r T connecting the two cups G and g may be 

 placed underground, and the electrical communication 

 between the balance and the electro-magnet E is easily 

 established at any distance desired. 



On the prolonged axis of the pulley A we may place a 

 rigid needle, and indicate by a simple transmission the 

 temperature on a large card placed outside. 



This apparatus has been constructed in a thoroughly 

 artistic manner by the able constructor, M. Redier. 



NEW ELECTRIC LIGHTS 



AN examination of the voluminous records of the 

 Patent Office discloses the fact that the activity in a 

 particular line of invention periodically waxes and wanes. 

 After slumbering for a number of years the problem of 

 procuring effective electrodes for the production of the 

 luminous electric arc has of late been revived, and with a 

 success hitherto unattained. The immediate cause of 

 this has probably been the recent improvements of 

 magneto-electric machines culminating in the Gramme 

 and the Siemens machines. An efficient source of elec- 

 tricity for the production of the light having been supplied 

 by these and other machines of a similar kind, a stimulus 

 was given to the invention of electrodes or wicks which 

 would employ the magneto-electric current to best advan- 

 tage in giving out light. The old faults of the carbon 

 points had never been quite overcome. The manufacture 

 of the points from soft-wood charcoal, fine coke dust, 

 lamp-black, calcined sugar, tar, resin, or mineral oil, cic, 

 had done much to render their consumption steady and 

 uniform ; and the regulators of Serrin and Dubosq had very 

 successfully overcome the widening of the luminous arc 

 by the wasting of the positive electrode. For large fixed 

 lights with several sets of luminous points, such as are 

 employed as beacon-lights on land or at sea, the ordinary 

 carbon points thus improved answered very well, but for 

 the purposes of general illumination they are still defect- 

 ive. To give a light suitable to a room or hall the 

 points require to be small, and any inequalities in their 

 action are very discernible in the light. One great diffi- 

 culty to be overcome, too, is the division of the light. 

 How to cause the current from a powerful magneto- 

 electric machine to produce a number of separate small 

 lights, such as would be essential for the lighting of streets 

 or buildings ? If the different lights were all joined up 

 " in circuit " and tlie currrent sent through the whole 

 series one after another, the break-down of any one of the 

 series would extinguish the whole and plunge the street 

 or building into darkness. 



During the last thirty years there have been many 

 attempts made to secure good electrodes for the electric 

 light as well as devices for adjusting them. Electrodes 

 of spongy platinum, palladium, and iridium have been 

 used. Another plan was to make the positive electrode a 

 fine stream of mercury flowing from a funnel and break- 

 ing upon a negative electrode of carbon or platinum 

 placed underneath. An objection to these metals was 

 the coloured lights they produced owing to the incan- 

 descence of their vapours in the arc. The carbon elec- 

 trodes were given divers shapes, and various combinations 

 of carbon and metal electrodes suggested. For instance, 

 it was proposed to use bar electrodes emitting the light 

 from their sides, and also to fuse iridium between two 

 carbon electrodes. An ingenious plan for getting a steady 

 hght was proposed by Mr. Harrison in 1857. It con- 

 sisted in giving a rotary motion to the positive electrode 

 and pointing the negative electrode at right-angles to it 

 and giving the latter a motion of translation, so that fresh 

 surface of the positive carbon was always appearing in 

 front of the negative carbon. A similar idea was again 

 patented in 1874 by Messrs. Wildman and Whitehouse. 

 About twenty years ago there was a great deal of activity 

 in this direction, but up till quite lately the usual carbon 

 points have always been fallen back upon. 



Within the last five years, however, two notable new 

 lights have made their appearance, namely, the lights of 

 Lodighin and of Jablochkoff". M. Alexandre Nicolsvitch 

 Lodighin is a Russian engineer of St. Petersburg. His 

 plan was first publicly tried there in 1873, and patented 

 in England in the previous year. It is designed to faci- 

 litate the use of the electric light for general lighting 

 purposes. The great defect of the ordinary carbon points 

 is the flickering of the light caused by the consumption 



