3734 Walnut St., Philadelphia, July 17, 1902.
To the Editor:
—Thinking perhaps some of your readers might be interested in this instrument that measures the perspiration in relative humidity units and the surface temperature without pressure on the limbs, I enclose a photograph of it. When the thermometer is attached to the body the temperature can be read immediately by the nurse. The hygroscope is correctable by the color thai the cobalt ehlorid stained hygroscopic substance takes and is adjustable at the axis. The picture shows normal registration on both scales. The humidity mechanism is a spiral of very fine copper to which is attached a siili membrane dipped in ehlorid of cobalt and coated with gelatin. The instrument is made of aluminum, of interchangeable aseptic parts, has a snap hinge and removable cover and is two inches in diameter. With careful attention, the instrument is correct enough to give some very interesting results, such as in