Abbé Refractometers
C. Zeiss, Jena #10088; Bausch & Lomb, Rochester, N.Y. #10200
This type of refractometer, devised in 1869 by Ernst Abbé, offers a rapid method of measuring the index of refraction of a liquid. A drop or two is placed between a pair of high dispersion prisms and the telescope is rotated to find the line of demarkation between light and dark at the critical angle. This is the largest angle of incidence for which total internal reflection takes place at the liquid-glass interface. This angle is a function of the index of refraction of both media. A scale is calibrated to read the refractive index directly. These refractometers are extensively used in drug, paint, and oil industry laboratories as well as in distillaries and dispensaries for analyzing such things as the percentage of fat in milk or the quantity of albumin in blood.
References: Eimer and Amend Catalog BCM 1927, p.664-66; Richard A. Paselk, Bulletin of the Scientific Instrument Society 62 (September1999) p.19-22; Gerard Turner, Nineteenth-Century Scientific Instruments, Berkeley, 1983, p.222.

Pulfrich Refractometer #10052
Unsigned, possibly by Zeiss
Like the Abbé refractometer, the Pulfrich measures indices of refraction by a determination of the critical angle for internal reflection, but it is adapted for use with solid as well as liquid samples. The dispersion can be measured by using as light sources the C and F lines in the hydrogen spectrum and the D line of sodium.
Reference: Arthur C. Hardy and Fred H. Perrin, The Physical Principles of Optics, New York, 1932, pp.359-62.

Hefner Lamp #10677
A. Krüss, Hamburg, Germany
This lamp, which burns amyl acetate, was developed about 1893 by Friedrich Hefner-Alteneck, an engineer at Siemens, and was used as a standard light source by the Physikalisch-Technische Reichsanstalt (Germany’s bureau of standards). It is furnished with an optical flame-measuring apparatus.
References: Max Kohl Catalogue No. 100 (c.1927) p.391; David Cahan, An Institute for an Empire, Cambridge, 1989, pp. 107, 116.

Photometers #10040
A.Krüss, Hamburg, Germany
The intensities of light sources are measured by comparing the illuminations produced by the unknown source with that of a standard source. Their relative distances are adjusted until the two illuminations at the photometer are equal. Because illumination from a point source obeys the inverse square law, the ratio of intensities is equal to the inverse ratio of the squares of the distances. Photometers, the devices that make the comparisons, come in various forms, two of which are exhibited here. The flicker photometer alternately flashes the two illuminations on a surface and as the distances are varied the eye can easily pick out the position of equal illumination when the flickering disappears. The other, known as a Lummer-Brodhun photometer, has a mirror system to allow the observer to simultaneously view both sides of a white surface, each occupying a portion of the field of view.
Reference: Max Kohl Catalogue No. 50 (c.1911) p.469; Eimer & Amend BCM Catalogue (1927) p.314; Robert Bud and Deborah Jean Warner, Instruments of Science: An Historical Encyclopedia, New York, 1998, pp.456-58.

Large Optical Disk and Refraction Tank #10700
Unsigned
The laws of elementary optics can be demonstrated on an optical disk. A narrow ray or set of rays of light shines along the surface of the disk and strikes a refracting or reflecting surface and graduations around the rim allow a measurement of the angles of incidence, reflection, and refraction. This disk has a carbon arc light source and a tank to hold water as the refracting medium. Because of its large size (54" high)it is easily visible to a large class of students.
Reference: Max Kohl Catalogue No. 100 (c.1927) p. 400-401.

Hand Mirror #10330
Unsigned
This mirror, with a frame and handle, illustrates the reduction in image size and the increase in the field of view of a convex mirror as compared to a plane mirror. Convex mirrors are used, e.g., as rear view mirrors in automobiles.
Reference: Central Scientific Co. Catalog F (1923) p.304.

Heliostat #10095
Unsigned
Heliostats are provided with a system of mirrors to direct sunlight into an apparatus needing bright illumination. A clockwork mechanism rotates the system so as to follow the apparent movement of the sun across the sky. D.B. Brace used a heliostat to supply illumination in his research on ether drift.
References: Max Kohl Catalogue No. 100 (c.1927) p.433; D.B. Brace, "On Double Refraction in Matter moving through the Æther," Philosophical Magazine, Ser. 6, 7, 317-29 (1904); Robert Bud and Deborah Jean Warner, Instruments of Science: An Historical Encyclopedia, New York, 1998, pp.305-8.

Kaleidoscope #10080
Unsigned
This optical device uses pieces of colored glass and mirrors to make geometric patterns that constantly change when rotated. Sir David Brewster (1781-1868), who is also known for his study of polarized light, patented the kaleidoscope in 1817.
References: Gerard L’E. Turner, Nineteenth Century Scientific Instruments, 1983 p. 297; Max Kohl Catalogue No. 100 (c.1927) p.393.

Carbon Arc Projector #10065
Duboscq, Paris
Lantern slide projectors were popular in the late 19th century not only with the general public but also with physics teachers who used them to demonstrate physical principles before a class. Armed with a set of carefully made slides, he could show many diagrams that would have taken much time to draw on the blackboard. They could also be used as sources of illumination in research projects.
References: Max Kohl Catalogue No. 100 (c.1927) pp.92-100; H.E. Roscoe, Spectrum Analysis, London, 1869, p.48.

Phosphoroscope #10743
Max Kohl Chemnitz ?
A pill-box shaped container is hinged on one side and opens to reveal a rotatable pair of connected disks with holes not aligned with each other. The material to be examined is placed stationary between the disks. A gear train (missing) rotates the disk assembly at high speed. A strong light source illuminates the substance momentarily through the holes in one disk and a short time later one can view the target through the holes in the other disk. If the target is phosphorescent it emits light after the illumination is cut off; if no light is seen, it is not phosphorescent. The duration of the phosphorescence can be gauged by changing the rate of rotation of the disks. Thanks to Paolo Brenni for his help in understanding the operation of this instrument.
References: This instrument is similar to the "Phosphoroscope after Becquerel" listed in the Max Kohl List No. 100, Volumes II and II on pg 424, item #89157. It is also described in several physics books such as P.A. Daguin, Traité élémentaire de Physique, (1862) Vol. 4, p.252.