Lectures on nervous diseases from the standpoint of cerebral and spinal localization, and the later methods employed in the diagnosis and treatment of these affections . equal parts Fig. 151.—A Diagram hesignkd to Illustkate the Method of Tangent Calibration.—The distances marked upon the straight hne are uniform. When they are joined by iin- ?aginary lines with the centre of the circular dial, these lines intersect its circumference atpoints which steadily tend to approach each other; hence the first milliampere will producea needle deflection which may exceed that produced by ten or more mil
Lectures on nervous diseases from the standpoint of cerebral and spinal localization, and the later methods employed in the diagnosis and treatment of these affections . equal parts Fig. 151.—A Diagram hesignkd to Illustkate the Method of Tangent Calibration.—The distances marked upon the straight hne are uniform. When they are joined by iin- ?aginary lines with the centre of the circular dial, these lines intersect its circumference atpoints which steadily tend to approach each other; hence the first milliampere will producea needle deflection which may exceed that produced by ten or more milliamperes in someother part of the dial. The more sensitive the needle, the greater will be the distancesmarked upon the straight line, and the dial also, on either side of the zero point; hence a verysensitive needle, balanced so as to avoid imnecessary Iriciion, will record eighths and quar-ters of one milliampere of current, if the coil be long enough. practically made by guesswork only. The scientific world has nowquite generally accepted the milliampere as the recognized standardof a unit of Fig. 152.—A Horizontal Milliampere-meter. (After the Thistleton pattern.) The screw-feet allow of .adjustment so as to insure a perfect leveling of the instrument. It is thenrevolved so that the needle (which will point north) rests at the zero point of the dial. Re-versal of the current diverts the needle to the opposite side One of the rheophoies showngoes to a binding-post of the battery, and the other to one of the electrodes employed uponthe patient. This instrument is very delicate, but the eye has to look down upon the dial inorderto observe the deflection of the needle. If the instrument is placed lower than the eye,this objection is not serious. With it it is easy to detect small fractions of a milliampere ofcurrent, and it is miirh less expensive than a good vertical galvanometer and more accuratethan most of those offered to the profession. I do not
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Keywords: ., bookcentury1800, bookdecade1880, bookidlecturesonne, bookyear1888
