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Integrating spheres are used extensively in reflectometers; therefore, it is important for the operator to be familiar with features that may lead to erroneous results during routine operation. This paper discusses an asymmetry present in the integrating sphere of the General Electric recording spectrophotometer, an excellent instrument widely used in reflectometry and color work.

The fractional sensitivity and operational refractive index range of the rod photorefractometer have been extended by physical modifications of axially symmetric refracting elements and the mode of illumination. Optical systems using conical and cylindrical rod elements with flat or spherical entrance ends illuminated by an axial light cone or a hollow annular light cone have been studied. Expressions describing the sensitivity of these configurations are presented, and typical numerical cases are computed on an IBM 650 computer. Extension of range to specimen index close to 1.0 permits the photorefractometer to detect index changes of low refractive index media. Experimental verification of the theory is achieved.

This paper presents the prototype of a hypodermic fiber-optics microscope. The instrument permits the researcher to observe tissues beneath the skin of the living animal or human, microscopically, through a hypodermic needle. The device utilizes fiber optics for image transmission, making it possible to observe through needles with inside diameters of 0.81 mm. Special features of this device include a self-contained illumination system within the same needle as the imaging bundle, and a unique microscope eyepiece which corrects for distortion caused by the necessary bevel at the far end of the needle. The resolving power of the present system is about 10 μ. A major problem is the definition of structures from each other within living tissue. Experiments are under way with various vital stains to improve this definition. Successful observations to date have been made of blood vessels and muscle fibers. Possible applications of the instrument are discussed.

A study of the extension of the rod and cone photorefractometer principle to the measurement of N and K, the real and imaginary parts of refractive index of absorbing fluids, is made. Theoretical analysis indicates high sensitivity in the low-absorption-coefficient region of the specimen when the illumination is incident at the interface at an angle close to the critical angle. Experiments are made on various rod configurations and results agree closely with theory.