From Hall’s Journal of Health, Volume 24, 1877, page 343.

“No physician questions the value of the spirometer for exercising and expanding the lungs, and for measuring their capacity. The great difficulty has been to find an instrument that can be compressed into a small compass when not in use, so that the physician or patient could carry it from place to place as circumstances might require. Another obstacle to the more general use of this truly valuable instrument has been its cost. The unwieldy spirometer of a few years ago, cost from $10 to $20.  Dr. Hall’s Portable Spirometer costs only six dollars and will be sent free to any address on receipt of the price by the editor of this Journal.

“It is 6 by 12 inches, and when closed it stands only 3 inches high and weighs less than 3 pounds.

“This cut represents Dr. Hall’s Portable Spirometer partly inflated, in order to show the manner of using it. When not in use it can ben closed together so as to occupy the small space above stated.  The scale and guide are hinged, so that they close down on the top of the spirometer, and occupy but little space.  The brass-work is plated with silver or nickel.”