A variety of devices for fastening the reflector on the head of the observer is in use, among which the head band, introduced by Cramer, will be found the most serviceable. It consists of a broad strap of some strong material which passes around the head and is fastened at the back by a buckle. To the part of the band or strap resting on the forehead is attached a padded plate, to which the reflector is fastened with its ball-and-socket joint (Fig. 2). The reflector usually either has a small hole in the centre or a small space in the centre is left unsilvered. This opening is intended to be brought before the pupil of one or the other eye of the observer in such a manner that the line of vision and that of light have exactly the same direction. Using the reflector in this way like the reflector of the ophthalmoscope, it is easier to obtain the image of the larynx well illuminated, but with the great disadvantage of {23} monocular vision, which makes all objects appear on the same plane and prevents a correct interpretation of distances--a very important point in laryngoscopy. It will therefore be found more advantageous to place the reflector on the forehead, and from thence reflect the light into the patient's larynx. Both eyes may thus be employed in viewing the laryngeal image, and a correct idea of the relations of parts in regard to distance may be formed. [Illustration: FIG. 2. Head Reflector.] The line of vision and the path of the beam of light in order to obtain the best results should be in the same plane as though the light emanated from the pupil of the observer; but practically the position of the reflector upon the forehead is nearly as good as when the hole in it is brought before the eye, because a line drawn from the pupil of the eye to the laryngeal mirror, and a line from the reflector upon the forehead to the mirror, do not form an angle sufficient to make any very great difference in the reflection of the light downward, and very little difficulty will be experienced in obtaining the desired image. The head reflector should be concave when artificial light or ordinary daylight is used, but be plane when direct sunlight is employed, for the concentration of the sun's rays by a concave reflector produces so much heat as to become painful to the patient. THE SOURCE OF LIGHT.--As an artificial source of light a candle, coal oil lamp, gas-flame, or incandescent electric lamp suffices for ordinary purposes. But frequently it is desirable to have a much stronger light than can be obtained without concentration, and several forms of apparatus for concentrating artificial light have been constructed and are in use. Among these, Tobold's lamp and Mackenzie's light concentrator are the most convenient and most universally used.