Mirrors

Mirrors, surfaces that give correct reflection of light. The opposite of mirrors are diffusing surfaces, which turn a correct (e.g. parallel) beam of light into scattered, or diffuse, light going in all directions. Correct reflection occurs when the irregularities of a given surface are smaller than the wavelength λ of the incident light. For vertical incidence, the size of the irregularities should not exceed λ/4, but for oblique incidence of rays, mirror reflection occurs even with significantly rougher irregularities. For almost grazing incidence, it is easy to observe correct reflection from filter paper, for example. The quality of mirror polishing should be higher the shorter the wavelength of light for which the mirror is intended; for example, for X-rays, whose wavelength is approximately a thousand times shorter than visible light, even the most perfect ordinary mirrors would turn out to be diffusing. The second quality usually required from mirrors is a high coefficient of reflection; therefore, metal (mercury, silver, etc.) is most often used as material for reflecting surfaces. The reflectivity of silver for yellow light is almost 96%, for mercury - 79%. However, in the ultraviolet part of the spectrum, these metals reflect significantly less: for a wavelength λ = 188 mμ, silver reflects only 22%, for example. A polished metal surface quickly tarnishes in the air; therefore, in most cases, a thin layer of metal is deposited on glass. Sometimes, however, if it is desirable to avoid reflection from the glass surface or when working with ultraviolet light (e.g. in mountain light lamps), use is made of unglazed metal reflectors. In optical instruments, prisms of total internal reflection are often used instead of metal mirrors (e.g. in cystoscopes). Flat mirrors only change the direction of the light beam, concave spherical or parabolic mirrors change the nature of the beam, making it converging (e.g. in the eye mirror), diverging, or parallel (spotlight mirror), and therefore can in many cases usefully replace lenses.

S. Vavilov. Medical Mirrors. Medical mirrors can be divided into three groups. The first group includes mirrors intended in the direct sense of the word for obtaining an image of the organ being examined, which is directly inaccessible to the examiner's eye. Mirrors for examining the oral cavity (see the illustration for the article Dental Instruments), pharynx, larynx (see the illustration for the article Laryngoscopy) serve this purpose. Mirrors for rhinoscopy are round or oval, of various diameters, in a metal frame, usually screwed onto a handle and can be easily replaced if broken. The handle directly at the mirror or along its length has bends of various sizes. For holding the epiglottis, there are mirrors with a holder (fig. 1), for examining the Eustachian tube - mirrors by Voltolini (fig. 2). The mirror by Duplé has an advantage over those mentioned; during examination, it can be given any position without changing the position of the handle (fig. 3). The disadvantage of these mirrors is the difficulty, bordering on impossibility, of sterilizing them by boiling due to their rapid deterioration and fragility. Therefore, recently mirrors of stainless metal have been proposed, which completely replace mirror glass, and most importantly - withstand sterilization by boiling (fig. 4). - The second group of mirrors has the purpose of reflecting incident rays from a light source onto the object to be examined or acted upon. This group includes frontal, eye mirrors (see the illustration for the article Ophthalmoscopy). - The third group consists of mirrors used as dilators or straighteners of natural openings, canals, and surgical wounds. Depending on the area of application, the mirror is given a corresponding name. In shape and size, mirrors of this category have great diversity. For brain operations, flat or spoon-shaped curved metal mirrors of various lengths and widths have been proposed. Some use wide spatulas or mirrors of hard rubber, which due to their elasticity traumatizes the brain less than metal mirrors (Adson).-For examination and operations in the nasal cavity, nasal mirrors are used, consisting of two spreading branches. The branches can be spread to the desired width at the examiner's discretion. The most commonly used are mirrors by Hartmann or Stepanov with springy handles (fig. 16) and Sologov-von Stein from springy wire (fig. 18). During examination, the patient is seated with the head tilted back slightly. The examiner with a frontal mirror is opposite the patient being examined. The light source is next to or slightly behind the patient. The mirror is inserted in the closed position and is opened only after insertion. Light, falling from the source onto the frontal mirror, is reflected and illuminates the nasal cavity. Before removal, the branches of the mirror should be closed. Before each use, the mirrors are thoroughly sterilized by boiling.-For examination of the external auditory canal, ear mirrors are used. They are made of hard rubber (Politzer), glass, and new silver. The latter are most commonly used. They have the appearance of a cone-shaped tube cut off at the apex (Hartmann, von Stein; fig. 13). Usually there are 3-4 sizes. The examination is conducted similarly to the examination of the nasal cavity, only the patient is in the lateral position. The mirror, previously sterilized by boiling and cooled, is inserted while pulling the auricle backward. The light is reflected from the frontal mirror. For examination of the inner ear, mirrors by Blake can be used (fig. 8). Mirrors for examining the esophagus - see illustration for the article Esophagoscopy.-For operations in the abdominal cavity, trough-shaped or flat, curved at an angle mirrors are widely used (see illustration for Gynecological Instruments). Their purpose is mainly to expand the edges of the wound, but the illumination of the operative field by rays reflected from the mirror is also important, especially with artificial lighting. Therefore, some mirrors are equipped with lighting devices (Ott; see illustration for Gynecological Instruments). The most convenient are disassembled mirrors having a handle and several of different lengths and widths, fastened with a lock (fig. 9). At any moment of the operation, one or another mirror can be used depending on the width and depth of the surgical wound. These are so-called hand mirrors. The inconvenience of using them is the need for an extra assistant during the operation. To eliminate this, various automatic mirrors with rack-and-pinion systems, with suspension of a weight, on a frame (see illustration for Gynecological Instruments) have been proposed.-In this respect, automatic mirrors for operations in the chest cavity are extremely convenient. They consist of two branches moving by a screw, which open the wound to the desired width without unnecessary trauma (Tuffier, Lilienthal; fig. 10). A similar device has the mirror proposed by Mayo for operations on the appendix (fig. 17). For operations on the bladder, automatic mirrors of two short, straight branches (Judd-Masson; fig. 12) or three curved, spreading ones (Walther; fig. 11) have been proposed. Of the hand mirrors for the bladder, the most commonly used are mirrors by Legue, Granat, and Jung (fig. 5-7). (Vaginal and uterine mirrors - see illustration for the article Gynecological Instruments.) For examining the female bladder, there are mirrors in the form of a tube with an obturator (Kelly) or trough-shaped with a light bulb (Ott). At present, with the appearance of cystoscopes, they are not used. Similarly, with the introduction of urethroscopy, the mirrors proposed for the urethra have been abandoned.-Mirrors for examining the rectum are arranged in the form of a tube with an obturator and in the form of spreading solid (Subbotin; fig. 15) or forked branches (Sims; fig. 14). Before use, mirrors are well sterilized by boiling. When inserted into the rectum, they are greased with petroleum jelly. Their use is limited only to the lower ampullary part of the rectum. For examining the higher parts, rectoscopy is used.

D. Bakulev. Mirror production. Until the end of the 19th century, mirror production was considered one of the most harmful due to the exceptional prevalence of mercury poisoning among workers engaged in it. Mercury had been used for silvering mirrors since the middle of the 15th century, and the production process was such that, despite the most stringent protective measures, it was almost impossible to avoid poisoning. The work process was described by contemporary specialists as follows: 'The silverer places a tin sheet on a special table with a marble top and side grooves, pours a little mercury on it, and rubs it in—an amalgam is obtained; then he pours mercury again to a height of 25 mm, places a paper sheet on it, and then glass; he pulls out the paper sheet from under the glass and places weights on top—the excess mercury flows into the side grooves. Then he tilts the table (again for the outflow of mercury), and finally the mirror goes for drying.' As can be seen from this description, the silverer had to deal with a huge amount of mercury spread over a large surface and giving off a mass of vapors. Renk calculated that during 8 hours a worker inhales 4.5 mg of mercury in the form of vapors and with dust—2.55 mg. How dangerous this amount is is evident from the fact that even hundredths (and according to more recent data—thousandths) of a milligram of mercury, introduced into the body constantly for many years, is already capable of causing chronic poisoning (see Mercury). In the 19th century, mirror production was particularly strongly developed in the city of Fürth (near Nuremberg), and it was studied there by many physicians (Kussmaul, Renk, Wollner, Schonlank). How great the number of poisonings was is shown by the following figures: for 1879-83, 123 cases of mercury poisoning were registered in Fürth, mostly severe; while the number of silverers working simultaneously did not exceed 170-180 people. According to Wollner's data, during the first two years of work 21% of silverers fell ill, from the 2nd to the 6th year—61%, from the 6th to the 10th—15%, etc. Due to the great noise raised in the press and the persistence of physicians Wollner and Schonlank, it was possible to pass a special mandatory decree in Prussia in 1889, somewhat amended in 1893. This decree did not prohibit the use of mercury, but, requiring the implementation of significant sanitary measures, made the production unprofitable. As a result, industrialists were forced to switch to another production method—silvering with silver (this method was invented in 1843 by Drayton and improved by the famous chemist Liebig). With the gradual transition of mirror production to the new silvering method, the number of poisonings began to decrease rapidly within the next few years; after 1891, only isolated cases were registered in Fürth, and from 1907 there were none at all. The situation was similar in England, Austria, France, and other countries, and now the mercury method of silvering mirrors there represents only historical interest. In Russia, the best description of artisanal mirror workshops was made for the Moscow province by Prof. Erisman in 1879. The working conditions in them were extremely unsanitary, all silverers and dryers suffered from mercury poisoning in a strongly expressed form, with cachexia and nervous phenomena. In large factories, the conditions were approximately similar to foreign ones. Small workshops and larger factories also switched to silvering with silver about 20 years ago. The course of the modern production process is approximately as follows: cutting (preparing the glass to size), edge grinding, surface polishing, silvering, coloring, cleaning, finishing. Grinding is done wet, with water splashes with small particles of sandstone, pumice, and mumiya flying into the air. During polishing, a small amount of pumice dust is released. During silvering, which is done by pouring complex compositions onto the glass surface (tin chloride in HCl; silver nitrate, ammonia, caustic soda in distilled water, nitric acid, sugar), ammonia vapors are released, and the temperature is slightly elevated. During coloring, the smell of oils (oil varnish, turpentine, oil lacquer, etc.) is released. During cleaning, a significant amount of pumice dust enters the air. In general, the harmfulness in modern mirror production is not particularly great.