52S 



NA TURE 



\Sei>t 28, 1882 



several lamps in series. It is brought into play by the 

 switch, C r>, which can be placed at E or D. When it is 

 at E, the negative terminal, A, is in communication with 

 the positive terminal, B, through the resistance, R, which 

 equals the resistance of the lamp, which is therefore out 

 or circuit. Whe 1 it is at D the cut-off acts automatically 

 to do the same thing when required. This is done by a 

 solenoid, v, which has two coils, the one of thick wire 

 offering no resistance, and the other of 2000 ohms resist- 

 ance. The fine wire connects the terminals, a' and B. 

 The solenoid has a movable soft iron core suspended by 

 the spring, U. It has a cross piece of iron which can dip 

 into two mercury cups, G and K, when the core is sucked 

 into the solenoid. When this is the case, which happens 

 when any accident occurs to the lamp, the terminal, a, is 

 placed in connection with the terminal, B, through the 

 thick wire of V and the resistance, R, in the same way as 

 it was done by the switch, c D. 



Electrical Arrangement. — The mode in which several 

 lamps arc connected up in series is shown by Fig. 6. M is 

 the dynamo-machine. The + lead is connected to B! of the 

 balance, it then passes to the lamp, l, returning to the 

 balance, and then proceeds to each other lamp, returning 

 finally to the negative pole of the machine. When the 

 current enters the balance it passes through the coil, S, 

 magnetising the iron core and drawing it downwards 

 Fig. 4). It then passes to the lamp, L l', through the 

 carbons, then returns to the balance, and proceeds back 

 to the negative terminal of the machine. A small portion 

 of the current is shunted off at the point, r, passing 

 through the coil, s', through the contact spring, T N, to 



the terminal, a', and drawing the iron core in opposition 

 to s. The carbons are in contact, but in passing through 

 the lamp the current magnetises the electromagnet, M 

 (Fig. 2), which attracts the armature, AB, that bites and 

 lilts up the rod, T, with the upper carbon a definite and 

 fixed distance that is easily regulated by the screws, v v. 

 The arc then is formed, and will continue to burn steadily 

 as long as the current remains constant. But the moment 

 the current falls, due to the increased resistance of the arc, 

 a greater proportion passes through the shunt, s' (Fig. 4), 

 increasing its magnetic moment on the iron core, whilethat 

 of s is diminishing. The result is that a moment arrive, 

 when equilibrium is destroyed, the iron rod strikes smartly 

 and sharply upon the spring, N T. Contact between T and 

 H is broken, and the current passes through the electro- 

 magnet of the break in the lamp. The break is released for 

 an instant, the carbons approach each other. But the same 

 rupture ol contact introduces m the shunt a new resistance 

 of considerable magnitude (viz. 1200 ohms), that of the 

 electromagnets of the break. Then the strength of the 

 shunt current diminishes considerably, and the solenoid, 

 S, recovers briskly its drawing power upon the rod, and 

 contact is restored. The carbons approach during these 

 periods only about - oi to '02 millimetre. If this is not 

 sufficient to restore equilibrium it is repeated continually, 

 until equilibrium is obtained. The result is that the car- 

 bon is continually falling by a motion invisible to the 

 eye, but sufficient to provide for the consumption of the 

 carbons. 



The contact between N t and H is never completely 

 broken, the sparks are very feeble, and the contacts do 

 not oxidise. The resistances inserted are so considerable 

 that heating cannot occur, while the portion of the cur- 

 rent abstracted for the control is so small that it may be 

 neglected. 



The balance acts precisely like the key of a Morse 

 machine, and the break precisely like the sounder-receiver 

 so well known in telegraphy. It emits the same kind of 

 sounds, and acts automatically like a skilled and faithful 

 telegraphist. 



This regulation, by very small and short successive 

 steps offers several advantages : (1) it is imperceptible to 

 the eye ; (2) it does not affect the main current ; (3) any 

 sudden, instantaneous, variation of the main current does 

 not allow a too near approach of the carbon points. 



Let now an accident occur, for instance, a carbon is 

 broken. At once the automatic cut-off acts, the current 

 passes through the resistance R instead of passing through 

 the lamp. The current through the fine coil is suddenly 

 increased, the rod is drawn in. contact is made at G and 

 K, and the current is sent through the coil, R. As soon 

 as contact is again made by the carbons, the current in 

 the coil S is increased, that of the thick wire in V di- 

 minished, and the antagonistic spring, U, breaks the contact 

 at G and K. The rupture of the light is almost invisible, 

 because the relighting is so brisk and sharp. 



I have seen this lamp in action, and its constant steadi- 

 ness leaves nothing to be de-ired. W. H. Preece 



THE SANITARY INSTITUTE 



THE Inaugural Address delivered by Captain Douglas 

 Galton at the opening of the Congress of the Sani- 

 tary Institute of Great Britain at Newcastle-upon-Tyne, 

 traces the growth of the more important questions relating 

 to public health and to the prevention of disease from 

 remote times down to recent date, and it is, both his- 

 torically and otherwise, of much interest. Questions of 

 public health have for many years past received increasing 

 attention in this and other countries, and the energies of 

 some of the ablest intellects have been devoted to the in- 

 vestigation of the various circumstances which tend to 

 injure the health of communities. Some have dealt with 

 the subject from a purely scientific point of view, others 

 have given their attention especially to the defects in 

 works of construction, such as systems of sewerage and 

 water-supply, which have led to the spread of disease, and 

 many physicians have devoted them elves exclusively to 

 those branches of medical science which deal with pre- 

 ventive as opposed to curative medicine. Captain Galton 

 refers to many of these researches, and shows how they 

 have tended to secure for us our present knowledge. Dr. 

 Tyndall's well-known investigations as to the existence of 

 low forms of life in the dust contained in air, and his 

 studies on putrefaction are recorded, as also Dr. Bastian's 

 and Mr. Lister's kindred labours, and the practical 

 applications to which they may be put. The several dis- 

 coveries as to the connection of disease with definite 

 organisms are noted; Professot Koch's recent con- 

 tributions as to the organisms associated with tuber- 

 cular disease closing this subject, in point of time. 

 M. Pasteur's discoveries in connection with fowl- 

 cholera and anthrax in cattle, and the associated 

 question of the attenuation of the infectious property of 

 the virus of these diseases, as the result of the processes 

 to which they are subjected are dealt with in some detail. 

 As to accepting M. Pasteur's conclusions in their entirety, 

 it may however be desirable to await further experiments, 

 the more so as certain investigations of Dr. Klein, an ac- 

 count of which has recently been submitted by the Local 

 Government Board to the Veterinary Department of the 

 Privy Council, have tended to conclusions adverse to the 

 general adoption of M. Pasteur's proposal to inoculate 



