1879.] Dr. B. W. Richardson on the Audiometer. 



65 



It measures also the electrostatic capacity of Lejden jars or con- 

 densers, and is sufficiently sensitive to appreciate and measure a surface 

 of tinfoil not larger than 4 inches square, the condenser being simply 

 placed between the wires of one pair of coils, and the disturbance pro- 

 duced being measured on the sonometer. 



I could cite many more interesting experiments in other branches 

 of physical research for which this instrument offers a wide field of 

 observation ; but my object this evening is neither to broach new 

 theories nor to correlate at present the results obtained with views 

 already advanced by Ampere and others. 



My only desire has been and is to show the wide field of research 

 the instrument opens to physical inquirers. I trust that in more able 

 hands it may serve to elucidate many physical phenomena. 



IV. " Some Researches with Professor Hughes' new Instrument 

 for the Measurement of Hearing; the Audiometer." By 

 Benjamin Ward Richardson, M.D., LL.D., F.R.S. Re- 

 ceived May 14, 1q79. 



Professor Hughes having done me the honour to show me first his 

 newly invented instrument for the measurement of hearing, and having 

 supplied me with an instrument for the purpose of testing the applica- 

 tion of it for physiological and practical purposes, I have been enabled 

 to make a considerable number of experiments, on which I venture to 

 submit the following preliminary report : — 



The instrument, as it has been used, is before the Society. It con- 

 sists of two Leclanche's cells for the battery, a new and simple micro- 

 phonic key connected with the cells and with two fixed primary coils, 

 and a secondary or induction coil the terminals of which are attached 

 to a telephone. The induction coil moves on a bar between the two 

 fixed coils, and the bar is graduated into 200 parts, by which the 

 readings of sound are taken. The graduated scale is divided into 

 20 centims., and each of these parts is subdivided into 10, so that the 

 hearing may be tested from the maximum of 200 units to 0°— zero. 

 The fixed coil on the right hand contains 6 metres of wire ; the fixed 

 coil on the left hand contains 100 metres. By this means a long scale 

 from the left hand coil is produced. The secondary coil contains 100 

 metres of wire. 



In using the instrument, one Leclanche's cell has been found suffi- 

 cient, as a general rule, but two have been used in instances where 

 the hearing of the person under test has been very defective. The 

 Leclanche cell was selected by Professor Hughes as affording a reliable 

 current for the purposes he had in view, and for standard comparisons. 



VOL. XXIX. F 



