example F1 is illuminated by the beam of light reflected by the surface R1 and the other half F2, of light from the surface R2. By varying the brightness or intensity of 5one or both of the beams which compose the two halves of the field, the dividing line D will disappear when the intensities of the beams are made equal. A wedge shaped piece of optical glass W is interposed 10between the objective L2 and the ocular slit S2 and is movable longitudinally of the telescope. The wedge deflects the rays of light upwardly, so that instead of the rays passing through the telescope substantially 15parallel to the axis thereof, they are inclined to the axis as illustrated diagrammatically by the dot and dash lines in Figs. 3 and 4. As the rays which pass through the telescope are deflected upwardly by the 20wedge in the constructional example illustrated in Figs. 2 to 4 inclusive, any rays which would lie above the optical axis would not be directed to the slit S2, no matter to what position the wedge might be moved, 25therefore the dispersion prism P2 is adjusted so that the dispersed beam will be projected by the telescope objective L2 slightly below said optical axis, as shown by the dotted lines in Figs. 3 and 4.
30With the wedge in the position shown in Figs. 3, the red rays are brought into coincidence with the ocular slit, while the remaining rays are lost within the telescope. When the wedge is moved to the position 35shown in Figs. 4, the violet rays pass to the ocular slit, By moving the wedge between. the extreme positions shown in Figs. 3 and 4, any particular section of the spectrum 40may be investigated by the observer, depending upon the position of the wedge. If the telescope is provided with a scale having marks to indicate wave lengths, and the wedge with a co-operating pointer, or vice 45versa, the wave length of the light ray under investigation may be immediately determined by a direct reading.
In order to compare the brightness of the two-beams of light reflected by the surfaces 50R1, R2, the light source or lamp L of the photometer is moved between the two surfaces until the dividing line D of the photometric field disappears. By providing the photometer with a pointer and a scale, 55divided to indicate ratio of the squares of the distances of the lamp from the reflecting surfaces R1, R2, the intensity or brightness of the reflected beam under investigation may be determined by a direct reading.
60Having explained the principles upon which the construction of my improved spectrophotometer is based, I will now describe the constructional details of the embodiment shown in Figs. 6 and 7. The numeral 10 65indicates a suitable base or support upon which is mounted, adjacent to one end thereof, a U-shaped bracket consisting of a bottom 11 and side walls 11a, 11b. The bottom 11 of this bracket is provided with a pair of parallel spaced rails 12, upon which the lamp carriage 13 is slidably mounted; 70roller's 14, 15 preferably being provided for supporting the carriage on said rails. A lamp socket 16 secured on said carriage is adapted to receive the lamp 14, the filament 18 of which is arranged perpendicular with the75 rails 12 and parallel to the parallel planes of the reflecting surfaces R1, R2. For convenience in moving the lamp between the surfaces R1, R2, I provide the lamp carriage 13 with a rack 19, in mesh with a pinion80 20, secured to a shaft 21. The shaft 21 is mounted in suitable bearings, as at 22, 23, and has its front end provided with a knurled operating handle 24. The side walls 11, 11a are coated, or otherwise 85constructed, to be practically non-reflecting and are provided with the apertures 25 arranged in alignment with each other and the lamp filament. Secured to the side walls, on the outer faces thereof, are the standard and90 sample holders 26, 27, each of which is provided with a spring pressed follower 28. Upon placing within one of the sample holders, as for instance the holder 26, a suitable standard such as a block of magnesium 95carbonate which is usually taken as a standard for 100% reflection, and placing within the other holder 27, a sample, the reflective power of which it is desired to examine, the amount of light reflected by each surface can100 be made equal by moving the lump as required. For convenience jn determining the comparative intensity, the photometer is provided with a scale and an index or pointer. As shown, the scale 29, graduated to105 indicate percentages or reflection ratios, is secured to the carriage 13 and is so located that the ratio of unity, or 100%, will coincide with the pointer or index 30 when the lamp is midway between the walls 11a, 11b.120
A portion of the light reflected from the surfaces R1, R2 of the objects placed within the holders 26 and 27 is collected by the ray directing prism P1, clamped upon a stand 31 a short distance from the entrance slit S2125 of the collimator C, and such light is directed through the slit S1 to the collimator lens or objective L2.
The collimator may be supported in any suitable manner, as for instance, by a pair of130 sleeves 33, secured to a bracket 34, the latter being attached to the front end of the base 10.
The usual dispersion prism P2 is mounted between the adjacent ends of the collimator and telescope and may be supported in any135 suitable way. The position of the parts are preferably such that the spectrometer telescope T, as shown in Fig. 7, is extended upwardly at an angle to the horizontal so as