470,638. Photo-electric apparatus for examining and sorting documents; valve relay circuits. BLUMENTHAL, L. J., and FREEDMAN, P. Jan. 17, 1936, No. 1603. [Classes 40 (iii) and 40 (v)] Consists in a method of and means for examining and sorting documents, such as ballot papers or competition coupons, according to the arrangement of symbols such as numerals or letters in selected positions in columns on the document or a page or sheet thereof. Each sheet is examined by comparing it with a standard sheet, on which the markings have been made in predetermined arrangement, and the comparison is effected by simultaneously scanning the sheet under examination and the standard sheet, each by a line of light, photoelectric cells corresponding in number and arrangement to the columns being so located that they are responsive to the scanning light beams. There is an " observer cell " for each column of the examined sheet, and a " standard cell " for the corresponding column of the standard sheet. Each such pair of cells co-operate to produce a certain electrical effect only when the same symbols occur in corresponding positions on the two sheets. If and when a predetermined number of these effects occur during the scanning, a device such as a gridcontrolled discharge tube is brought into action, and operates sorting-mechanism. Fig. 1 shows how the examined documents 9 may be scanned by carrying them by means of a belt 8 past a line of light 15 produced by a lamp 11 and cylindrical lenses 13. A coloured light filter is arranged at 14. A set of " observer " photo-electric cells 19 is provided, one for each column on the document, and light reflected from the latter modulated in accordance with any symbols which may appear in the columns, passes through lenses 16 and is directed by silica rods 17 on to the cells. Simultaneously the standard document 21, Fig. 2, is scanned by locating it below a belt 81 in which slits 20 are provided to allow light from a lamp 22 to fall on the document. The belt 8<1> moves synchronously with the conveyer belt 8. An optical system similar to that shown in Fig. 1 enables light reflected from the columns of the document 21 to fall on the " standard photocells (not shown). A further system of photo-electric cells, not shown in Fig. 1, described as "volume control photocells," is so arranged as to be acted upon by light from a special source which uniformly illuminates the whole of a sheet under examination whilst it is being scanned by the line of light 15, this auxiliary light being such as to have no effect on the " observer " cells 19. The purpose of the " volume control cells " is to ensure that the modulating effects produced by the symbols on any given document will be independent of the quality of the ink &c. used for the symbols, or the density of the imprints constituting the symbols, provided they are uniform throughout that document. In Fig. 5 is shown a system whereby in comparing one column on an examined sheet with the corresponding column on a standard sheet, the photo-electric cells are utilized to operate a grid-controlled discharge tube T to operate sorting-mechanism which may embody features described in Specification 468,692. The system includes valves VO, VS controlled respectively by the " observer cell " PO and the " standard cell " PS (the valve VO being also controlled by the " volume control" cell PV), a bridge arrangement of rectifying valves D<1>... D4 connected to the valves VO, VS, and controlling a valve VC, a cathode-ray tube K, the deflecting plates d<1> of which are controlled by the valve VC, and a condenser C, a charge on which is built up by the action of the cathode-ray tube, which charge when of sufficient magnitude causes the discharge tube T to function and to operate a relay which actuates the sorting- mechanism. The general operation of this system is as follows. When a symbol on the document under examination is the same as that in a corresponding position on the standard document, the bridge D<1> ... D<4> is balanced, and no current flows along a resistance R<6>; if, however, correspondence between the symbols is lacking, a voltage drop occurs across R<6>, causing a decrease of current through the valve VC. This reduces the voltage drop in a resistance R<7>, and affects the potential difference between the plates d<1> of the cathode-ray tube K. There are two pairs d, d<2> of deflecting plates in the tube K, the pair d<2> being controlled by a " switching photocell " P (not shown in Fig. 1), which operates only during the scanning of a sheet. The tube K is so constructed that the cathode beam can reach the collector electrode e only when appropriate potentials are applied to the plates d<1>, d<2>, this condition occurring only when the currents through the cell P and the valve VC are at their maxima. Thus, each time the symbols in the observed and standard documents are identical, the cathode beam is enabled to reach the plate e, and a charge is imparted to the condenser C. When the charge so accumulated is sufficient (as determined by the presence of a sufficient number of correctly placed symbols on the examined document), the discharge tube T operates, and the consequent voltage drop in a resistance R<10> in its anode circuit causes an oscillating valve (not shown) to function, whereby the sorting mechanism is operated. Means comprising a photo-electric cell PZ co-operating with a special valve VZ are provided for neutralizing any residual charge on the condenser C after the scanning of each sheet. The cell PZ is operated by light passing through apertures or the equivalent in the moving conveyer band at points intermediate between the documents. A modified circuit arrangement is described, Fig. 6 (not shown), in which the " standard valve " VS has two control grids, and is controlled by the " volume control cell " PV. An electrical system such as shown is provided for each column on an observed document and for the corresponding column on the standard document. Any one of such systems may control the delivery of selected documents into a separate receptacle, or several such systems may operate conjointly.