Discoveries and Inventions of the Nineteenth Century

the surface of a revolving cylinder of polished steel, where the place is shown by the spot they leave on the metal. M. Pouillet’s chronoscope dispenses with the revolving cylinder, and measures the duration of the current established by the projectile at one part of its course and cut off at another, by the arc through which the needle of a galvanometer is impelled. The instrument which has been most employed in this country by artillerists is that invented by Professor Bashforth. Its indications are extremely accurate, for readings may be taken to the two-thousandth part of a second. From ten to fifteen screens are placed in the path of the projectile at distances asunder which may vary from 15 ft. to 150 ft., but which, of course, are carefully measured. Each screen is formed of a wire 660carrying an independent current, which also circulates in the coils of an electro-magnet. The ten electro-magnets have styles attached to their armatures in such a manner that when all the currents are passing, ten parallel spiral lines are traced on the surface of a vertical revolving cylinder, about 12 in. long and 4 in. diameter. The cylinder is covered with a sheet of highly-glazed paper coated with lampblack; and when the sheet is removed, the lampblack may be fixed on the paper if desired, and the record made permanent. The equal intervals of time are marked on the same cylinder by another electro-magnet connected with a pendulum beating half-seconds. The axis of the revolving cylinder, &c., carries a heavy flywheel, which is set in motion by the hand at the rate of about three revolutions in two seconds, and the rest of the mechanism is thrown into gear just before the signal to fire is given. The arrangement of the electric connections at the screens is such that at the moment of the rupture of the wire, the circuit is broken for an instant only. At this moment, the iron of the corresponding electro-magnet ceasing to attract its armature, the latter is drawn away by a spring; but the re-establishment of the current immediately brings it back, and the style continues to trace the same spiral line as before. The passage of the ball through the screen is therefore marked by a little notch in the spiral line, thus, , and the point where the deviation begins indicates the time at which the ball passed. In order to read off this time, a straight-edge is applied to the cylinder parallel to its axis; and by means of a scale sliding upon the straight-edge the distances between the notches on the several spirals are compared with those between the pendulum marks. To record the instant at which a projectile passes determined points in a cannon’s bore, lateral plugs are screwed in, each having, just projecting into the bore, a small steel ball, which, pressed outwards by the passing projectile, causes a cutter to divide the primary wire of a Ruhmkorff coil, whereupon the spark that passes in the secondary circuit leaves its record on a uniformly moving disc. Each plug has its own battery, coil, and disc. A special feature of recording instruments may be exemplified by certain applications of the principle to the investigation of physiological actions. A skilled physician is often able to detect in the pulse of his patient certain characteristics besides the mere rate, which are highly significant as regards the condition of the circulatory system. The range of these indications has been greatly extended by an instrument invented by MM. Chauveau and Marey, by which the pulse is made to write down a graphic representation of its action. The patient’s arm having been placed on a suitable support, a little stud covered with soft leather is lightly pressed against the artery by a spring. The stud is in contact with the shorter end of a very light lever, the other extremity of which is furnished with a point, which registers its movements on a cylinder of blackened metal, made to rotate and advance longitudinally by clockwork; or the record is taken on strips of flat smoked glass. As the motion is much magnified by the lever, every variation in the pressure of the blood in the artery during the beat of the pulse is distinctly and faithfully indicated. From the line so traced the physician may obtain infallible data for judging of the condition of the heart, the action of its valves, &c. It is marvellous to observe the manner in which the curves of the sphygmograph, as the instrument is termed, change their form when certain drugs are administered: the change in some cases occurs immediately, so that the eye can detect by the inspection of the sphygmographic curve almost the instant at which the 661drug was introduced into the system, and the nature of its action on the heart. Fig. 317.—Negretti’s Deep-Sea Thermometer. Another instrument which is doing good service in the hands of medical investigators is the spirograph, in which the rise and fall of the chest in breathing are similarly traced by the motions of a lever. In this instrument a small pad, which presses on the chest, communicates its movements to an elastic membrane, which, like the skin of a drumhead, covers one end of a cylindrical box maintained in a fixed position relatively to the person of the patient. The air in this box is in communication, by means of a flexible tube, with the interior of another similarly closed box; the elastic membrane of the latter acts against the short end of a lever, which is made to register its movements as in the sphygmograph, for the compression of the air caused by the rise of the chest is conveyed to the second box through the flexible tube. The curves furnished by this instrument also give valuable indications, and exhibit marked changes under any influence in the least degree affecting the respiratory system. The value of a self-registering instrument for solving problems, the intricacy of which is increased by the multiplicity and rapidity of the actions to be observed, cannot be better illustrated than by the success with which Professor Marey has thus studied some complicated actions of locomotion, as related in his extremely interesting work entitled, “La Machine Animale,” a translation of which has appeared in “The International Series.” The action of the horse in the various paces, walking, trotting, galloping, &c., has been an endless subject of discussion, with no other data than the shoe-marks left in soft ground, and the general appearance of the animal’s movements to an observer. But M. Marey—by means of elastic bags containing air, communicating the pressure through flexible tubes, so as to move little levers, which write their traces on a revolving cylinder impelled by clockwork, and carried by the rider,—has completely and finally settled all the points in dispute. It is now definitely known how the horse’s feet are placed on the ground in each of his paces, and the actual and relative time that each foot remains down. The instruments are also made to register the vertical movements of the animal, so that a complete record of its motion can be obtained. Fig. 318.—Negretti’s Deep-Sea Thermometer, general arrangement. It was long a difficulty to obtain data as to the temperature of the sea at great depths below the surface. It is obvious that the ordinary maximum and minimum registering thermometers would not give the temperature at any particular depth to which they might be submerged, 662but merely the temperature of the warmest or coldest stratum of water through which they passed in their descent or ascent. No plan which has been devised to obviate these difficulties appears to have been attended with success, until a quite recent invention of Messrs. Negretti and Zambra supplied the desideratum, and furnished a convenient instrument for trustworthy determination of the temperature of the ocean at any required depth. The same firm long ago constructed thermometers for deep-sea soundings, with bulbs protected from the pressure of the water by an outer covering of thick glass surrounding the delicate bulb of the thermometer, between which and the outer casing a space was left, partially filled with mercury, so that heat might readily pass to or from the inner bulb without the latter being exposed to the superincumbent pressure. The new recording deep-sea thermometer differs, however, from all other registering thermometers by containing mercury only, without alcohol, or springs, or other removable indices, and, consequently, it is free from liability to derangement. The following is the description of the instrument: In the first place it must be observed that the bulb of the thermometer is protected so as to resist the pressure of the ocean, which varies according to depth, that of 3,000 fathoms being something like 3 tons pressure on the square inch. The new instrument is in shape like a syphon with parallel legs, all in one piece, and having a continuous communication, as shown in Fig. 317. The scale of the thermometer is pivoted on a centre, and being attached in a vertical position to a simple apparatus (which will be presently described), is lowered to any depth that may be desired. In its descent the thermometer acts as an ordinary instrument, the mercury rising or falling according to the temperature of the stratum through which it passes; but so soon as the descent ceases, and a reverse motion is given to the line, so as to pull the thermometer towards the surface, the instrument turns once on its centre, first bulb uppermost, and afterwards bulb downwards. This causes the mercury, which was in the left-hand column, first to pass into the dilated syphon-bend at the top, and thence into the right-hand tube, where it remains, indicating on a graduated scale the exact temperature at the time the thermometer was turned over. The cut shows the position of the mercury after the instrument has been turned on 663its centre. A is the bulb; B the outer coating or protecting cylinder; C is the space of rarefied air, which is reduced if the outer casing be compressed; D is a small glass plug, as in Negretti and Zambra’s maximum thermometer, which at the moment of turning cuts off the mercury in the tube from that in the bulb, thereby ensuring that none but the former can be transferred into the indicating column; E is an enlargement made in the bend, so as to enable the mercury to pass quickly from one tube to another in revolving; and F is the indicating tube, or thermometer proper. When the thermometer is put in motion, as soon as the tube has acquired a slightly oblique position, the mercury breaks off at the point D, runs into the curved and enlarged portion, E, and eventually falls into the tube, F, as the instrument resumes its original vertical position. Fig. 319.—The Atmospheric Recording Instrument. The contrivance for turning the thermometer over at the bottom of the sea may be described as a vertical propeller, to which the instrument is pivoted. So long as the instrument is descending the propeller is lifted out of gear and revolves free; but as soon as the ascent commences, the action is reversed, the propeller falls into gear with a pinion connected with the thermometer, and by these means the thermometer is turned over, and after one turn it remains locked and immovable. The engraving, Fig. 318, shows the general arrangement, T being the thermometer, S a metal screw connected with the frame of the thermometer by a wheel-and-pinion movement at W; S† is the stop for arresting the movement of the thermometer when it has made one complete turn. 664The atmospheric recording thermometer (Fig. 319) differs from the deep-sea thermometer by not having the double or protected bulb, as it is not required to resist pressures. In this form of the instrument, the thermometer is turned over by a simple clock movement, which can be set to any hour that may be desired. It is fixed on the