Diseases of the larynx / by J. Gottstein ; translated and added to by P. M'Bride.

  • Jacob Gottstein
Date:
[1885?]
Catalogue details

Licence: Public Domain Mark

Credit: Diseases of the larynx / by J. Gottstein ; translated and added to by P. M'Bride. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    order to increase its intensity. For this reason we must use the image which is equal to the size of tlie flame or smaller, because a small ima»-c Fig. 7. Reflector and Forehead Band. contains more rays of light than a portion of a larger image. We get the image equal in size to the flame when the distance from the reflector alike to the larynx and to the flame is equal to twice the length of the focal distance. As the distance of the larynx from the reflector is given at about 30 centimetres, and as the position of the flame at a like distance from the observer can be arranged, we must use a reflector of 15 centimetres (focal distance) in order to thi-ow into the interior of the larynx an image equal in size to the flame. The diminished image of the flame lies without the focal distance and within twice the focal distance, and accordingly, in order to use it for illuminating purposes, the focal distance of the concave mirror must be more than 15 and less than 30 centimetres. Concave mirrors with a focal distance of from 15 to 20 centimetres are therefore the most suitable. In our calculations we have supposed that the briglitest light is thrown upon the glottis, and for the parts above and below it must, of course, be less, but still ahrays strong enough to be employed with advantage, more especially as we are enabled to correct tlie mistake by slightly clianging tlie distance of the examining eye from the mouth. Short and longsiglited persons w]io cannot accommodate their vision to the distance of 30 centimetres must use suitable glasses. It is evident on optical iwinciples that for the correct employment of the diminished