The experiments connected with the construction of this apparatus led to others with other substances than selenium, and also without the use of telephone or battery. A thin sheet of hard rubber was held close to the car while a beanm of intermittent light was thrown upon it by a lens, the result being the production of a _musical note, and this effect was intensified by arranging the hard rubber as a diaphragm and listening through a hearing-tube. The rethaskable though natural conclusion was reached " that sounds can be produced by the action of a variable light front substances of all kinds ?rhea in the form of thin diaphragms." Subsequently prof. Bell arrived at the conclusion that sono rousness sunder the influence of intermittent light is a property of all matter. Various experi ments were made with different fibrous and porous materials, such as cotton-wool, worsted, silks, sponge, lamp-black, etc. These articles were inclosed in a conical cavity, con tained in a piece of brass, and closed by a flat plate of glass through which an intermit tent beam of light was thrown upon them. A hearing-tube communicated with the cavity. Mr. Tainter found that the darkest shades produced the best effects. Black worsted especially gave an extremely loud sound. Cotton-wool darkened with lamp-black gave so loud a sound as to suggest the use of lamp-black alone. Of this substance a tea spoonful, placed in a test-tube and exposed to an intermittent beam of sunlight produced the loudest sound of all, and a piece of smoked glass, with the smoked surface receiving the intermittent beam, gave a fine effect. Upon smoking the interior of the conical cavity of the receiver above-mentioned, and then exposing it to the intermittent beam, "the effect was perfectly startling. The sound was so loud as to be actually painful to the ear placed closely against the end of the fsearing-tube." The various experiments above alluded to will probably be of great importance in telephony as indicating that lamp-black may be substituted for selenium in an electrical receiver. M. Mercadier passed ass intermittent beans from an electric lamp through a prism and found a coca in the audible effects in different parts of the spectrum. These experiments were repeated by prof. Bell, with somewhat different results. Under conditions not neces sary to describe here, "sounds were obtained in every part of the visible spectrum excepting the extreme half of the violet, as well as in the ultra-red. A continuous increase in the loudness of the sound was observed upon moving the receiver gradually from the violet into the ultra-red. The point of maximum sound lay very far out in the ultra-red. Beyond this point the sound began to decrease, and then stopped so suddenly that a very slight motion of the receiver made all the difference between almost maximum sound and complete silence." Removing the smoked wire gauze from the receiver and
substituting red worsted different results were obtained, the maximum effect being pro duced in the green at that part where the red worsted appeared to be black. On either side of this point the sound gradually died away. On substituting green silk for the red worsted the maximum effects were found in the red. A test tube containing the vapor of sulphuric ether was then substituted for the receiver, but no effects were observed till a certain point far out in the ultra-red was reached, when a musical tone was suddenly produced, which disappeared as suddenly further on. With the vapor of iodine the maximum effect was in the green. These, and experiments with other substances, led to the conclusion that " the nature of the rays that produce sonorous effects in different substances depends upon the nature of the substances that are exposed to the beam, and that the sounds are in every ease due to those rays of the spectrum that are absorbed by the body." These phenomena led prof. Bell to the construction of a new instrument for use in spectrum analysis, which was described and exhibited to the philosophical society of Washington last April. "The eye-piece of a spectroscope is removed and sensitive substances are placed in the focal point of the instrument behind an opaque diaphragm containing a slit. These substances are put in communication with the ear by means of a hearing-tube, and thus the instrument is converted into a veritable spectrophone.' Suppose we smoke the interior of our spectrophonic receiver and fill the cavity with peroxide of nitrogen gas. We have then a combination that gives us good sounds in all parts of the spectrum, visible and invisible, except the ultraviolet.i'Nro w pass a rapidly internmted beam of light through some substance whose absorption spectrum is to be investigated, and bands of sound and silence are observed upon exploring the spectrum, the silent positions corresponding to the absorption bands. Of course the ear cannot for one moment compete with the eye in the examination of the visible part of the spectrum; but in the invisible part beyond the red, where the eye is useless, the ear is invaluable. In working in this region of the spectrum, lamp-black alone may be used in the spectro phonic receiver. Indeed, the sounds produced by this substance in the ultra-red are so well marked as to constitute our instrument a most reliable and convenient substitute for the thermo-pile." See Science for May 28, 1881. Prof. Bell recognizes the fact that the spectrophone must always be no more than an adjunct to the spectroscope, but believes that it will have a wide and independent field of usefulness in the investigation of absorption spectra in the ultra-red.