November i, 1889.] 



SCIENCE. 



295 



as the Thompson electrical balance ; but the latter is an expensive 

 instrument, beyond the reach of the ordinary electrical engineer, 

 and is not readily portable. 



Professor Ryan's invention, consisting of a method of suspension 

 and the laying-off of a scale, renders the construction of the appa- 

 ratus a matter of a few hours' labor by any fair mechanic. 



As in the Thompson balance, the current passes through two 

 parallel fixed coils, and through a coil swinging between them. In 

 the Thompson balance the current passes into this swinging coil 

 through the suspension, consisting of a great number of fine copper 

 wires, which will conduct a large current, but at the same time 

 offers but little resistance to the movement of the swinging arm. 

 The mounting of these wires is a very laborious operation, which 

 adds greatly to the cost of the machine. Professor Ryan over- 

 comes this difficulty thus. From each end of the axis of the arm a 

 single silk thread extends upward through a hole in the hard-rubber 

 framework above. These holes are drilled at an angle with the 

 vertical, and the threads bearing on their upper acute edges form 

 what is practically a knife-edge suspension. The current is taken 

 into the coil by means of two broad strips of thin silver foil, fas- 

 tened at one end to the base, at the other to the arm near the axis. 

 This foil is so thin and light that it offers practically no resistance 

 to the swinging arm, but at the same time is capable of carrying a 

 very large current. 



The balancing of the coil-bearing arm is accomplished by the 

 movement of an arm carrying a weight and a pointer, and swing- 

 ing in the horizontal plane. This arm has the greatest moment 

 about the axis of suspension when it is perpendicular to it, and the 

 least when it is parallel to it. In moving from one of the positions 

 to the other, the pointer swings over a quadrant. 



The force tending to move the coil, and hence the moment re- 

 quired to balance it, must be proportional to the square of the 

 current. If on a line through the pointer pivot, and perpendicular 

 to the axis of suspension, distances be laid off proportional to the 

 squares of the currents, and perpendiculars be erected at those 

 points, the distances of their intersections with the arc of the quad- 

 rant from the axis of suspension will be proportional to the squares 

 of the corresponding currents. If these points be marked with the 

 square roots of their respective distances, the instrument will give 

 ■direct readings. 



Indicating Temperatures at a Distance. — For many 

 purposes it would be convenient if the temperature indicated by a 

 thermometer, in some situation not easily accessible, could be 

 telegraphed, as it were, to some spot convenient to the observer. 

 Many methods more or less successful have been devised ; and M. 

 Morin, a French inventor, as we learn from Engineering, has re- 

 cently patented another method, which, if of a somewhat limited 

 range of applicability, may nevertheless be useful in certain situa- 

 tions. In a few words, his apparatus consists of a thermometer, 

 with a scale about 8 inches long, reading from o" to 30° C. The 

 bore of the tube is about .02 of an inch in diameter, and the bulb is 

 constructed to hold about 7 cubic centimetres of mercury. A 

 platinum wire, with a diameter of about .0008 of an inch, runs 

 from one end of the tube to the other, being connected with plati- 

 num terminals fused through the glass. The length of wire com- 

 prised between the 0° and 30° marks on the scale has a resistance 

 of 200 ohms. The resistance of the whole thermometer, therefore, 

 will vary considerably as the mercury rises and falls in the tube, 

 and it is on this fact that the arrangements for telegraphing the 

 temperature to a distant point depends. The receiving instrument 

 consists of a low-resistance Deprez-d'Arsonval galvanometer, and 

 an auxiliary resistance of about 200 ohms. Two Leclanche cells 

 of large size connected in parallel, the electromotive force of which 

 is very constant for varying temperatures, are employed to send a 

 current through the thermometer, resistance, and galvanometer ; 

 and the deflection of the latter indicates the height of the mercury 

 in the thermometer-tube. 



Metal Sheets as Electrical Screens. — Professor O. 

 Lodge contributed a paper, at the recent meeting of the British 

 Association, " On the Failure of Metal Screens to screen off the 

 Electrostatic Effect of Moving or Varying Charges," which is in- 

 teresting, inasmuch as Maxwell suggested the bird-cage form as 



the best form of lightning-protector. Professor Lodge has found, 

 that, as long as a charge is stationary, the thinnest film of a con- 

 ductor is indeed a perfect screen. An ordinary wire gauze is also 

 impervious to electric disturbances from without, and so is a silver- 

 coated beaker, as long as the coating is not too thin. This was 

 investigated by placing a very light needle, highly charged with 

 opposite electricities at its ends, within the beaker. When, how- 

 ever, the coating became thinner and thinner, so that the resistance 

 of the silver film increased from a fraction of an ohm to 100 ohms 

 and more, and when the charged bodies were rapidly approached, 

 being shot towards the beaker sometimes, the needle was de- 

 flected, the deflections becoming measurable at 1000 ohms' re- 

 sistance. One may simply say that the protection ceased as soon 

 as the silver film became translucid, as Hertz has observed in his 

 classical researches. 



Automatic Electric Balance. — There has been exhibited 

 in Paris an electric balance, the invention of Mr. William Snelgrove. 

 The placing of the object to be weighed in the pan closes an elec- 

 tric circuit. The current along this circuit operates a motor at- 

 tached to the weight on the beam, causing it to run out on the 

 beam till an equipoise is established, when the circuit is broken. 

 When the pan is cleared, every thing returns to the original con- 

 dition. 



HEALTH MATTERS. 

 Chloroform as an Anaesthetic. 



A CONTRIBUTOR to The Lancet states that in the medical jour- 

 nals for the last ten years there are reported one hundred and 

 twenty (if not more) cases of death under chloroform. Many of 

 these are very imperfectly described, but in at least forty-nine cases 

 the patients were in good general health at the time of administra- 

 tion, and required an ansesthetic merely for the performance of 

 some minor operation ; e.g., extraction of teeth (eleven cases of 

 death), reduction of dislocations (nine cases), eye operations, fistula, 

 and so on. In some fifty-nine cases death occurred before the 

 commencement of the operation, and so was clearly due to the 

 chloroform alone. In about twenty of the cases it is noted that 

 chloroform had been successfully given on previous occasions, in 

 one as many as eight different times before the fatal administra- 

 tion. It is evident from the foregoing that chloroform is uncertain 

 in its action ; that not only do people die while under chloroform, 

 but also from it ; frequently, too, even when it is used by skilful 

 hands. Of course, it is possible to retort that "it was not properly 

 given," which may be correct. This will not alter the fact that 

 these accidents prove chloroform to be a powerful agent, very diffi- 

 cult to administer properly ; indeed, so difficult and dangerous that 

 it is scarcely suitable, for a routine anEesthetic, when a drug less 

 powerful for evil can replace it. 



The nauseous flavor and the sense of suffocation from ether can 

 be entirely done away with by the use of nitrous oxide, and its in- 

 halation made more agreeable than even that of chloroform, while 

 the patient quickly becomes unconscious without the struggling so 

 common with chloroform. The writer goes on to say, " I have not 

 yet found a single patient who has once inhaled ether preceded by 

 nitrous oxide complain of suffocation, or object to take it again on 

 the ground of its unpleasantness. 



" The readiness with which chloroform affects the heart, the 

 smallness of a fatal dose, and especially the ease and suddenness 

 with which such a dose can be inhaled, almost by a couple of deep 

 inspirations, will make its safe exhibition always a difficult task to 

 invariably accomplish. Having had many years' experience, I 

 have gradually come to believe chloroform to be a less safe anaes- 

 thetic than ether." 



Preventable Blindness. 



At a meeting of the Boston Society for Medical Observation, 

 April I, 1889, a paper was read by Hasket Derby, M.D., on this 

 subject. We have recently published the report of the Albany 

 committee on the increase in blindness. A certain proportion of 

 this loss of sight is preventable. Being desirous of estimating the 

 relative number of such cases in his own community. Dr. Derby 



