in 1911, and subsequently published The Imperial Peace and The Teaching of Paul in Terms of the Present Day (1913); Recent Research and the New Testament (1914); The Making of a University (1915) and the Life and Letters of William Black (1918).
RANOEGGER, ALBERTO (1832-1911), musical composer and conductor, was born in Trieste April 13 1832. He settled in
London in 1854 after holding various musical appointments in
Italy. Both as an orchestral conductor, and as a teacher of
music and singing he held for many years a leading position in
London. Besides conducting on various occasions at the Royal
Opera, musical festivals and elsewhere, he did much, as conductor
of the Carl Rosa company from 1879, towards the popular revival
of opera in England. He died in London Dec. 18 1911.
RANGE-FINDERS AND POSITION-FINDERS (see 22.888).
Recent improvements have rendered many of the earlier types
of range-finders obsolete, and the following features are com-
mon to all modern coincidence range-finders. The range-finder
usually consists of two main parts, viz: a strong outer tube
and an inner frame which supports the delicate telescopic
system, any slight derangement of which would seriously upset
the accuracy of the range-finder. The outer tube is made as
strong and rigid as possible, having regard to the weight which
can be allowed. The inner frame is supported in such a way that
any slight bending of the outer tube will not affect it.
Some form of double end reflector is always used. This at one time consisted of a pentagonal prism, but large pentag- onals are very costly; they absorb a good deal of light and are liable to slight distortion with changes of temperature. There is therefore a tendency to replace them by a combination of two silvered plane mirrors inclined to one another at 45, and either fixed in a mount made of a metal having the same coefficient of expansicn as glass, or rigidly attached to an upper and lower glass support, to prevent change in their relative positions.
The central reflectors usually take the form of two or more prisms balsamed together, and are known as the centre prism combination. Their object is to deflect the rays received through the two ends of the range-finder into the eye-piece, and to present the two images of the target in the field of view immedi- ately above and below a thin separating line. Their construction is usually rather complicated. The fine separating line is as a rule obtained by means of a special separating prism ; or by the edge of a silvered surface on one of the prisms, so arranged that the rays forming one image pass through the prism, and those forming the other image are reflected by the silvered surface.
The centre prism combination is also used for erecting or inverting the images, and for defining the limits of the fields of view received from each half of the range-finder. The arrange- ments of fields of view usually met with are the following:
1. The field of view is divided into two equal halves and the images in both are erect. When a coincidence has been made, the separating line cuts straight through the image of the target. This system is used with naval and coast defence range-finders which have to deal with targets having long vertical features, e.g. masts and funnels. It is known as the ' erect " system.
2. The field cf view is divided into two parts by the separating line. One field (in field range-finders usually the lower) is erect, and the other one is a replica of it, being inverted up for down but not right for left. With this system it is much easier to make an accurate coincidence on small targets, but it has the slight drawback that the total actual field of view is necessarily considerably smaller than with the erect system, and a slight elevation or depression of the range-finder may cause the target to pass the separating line and disappear. This, however, is not of much importance if the target is a stationary or slowly moving one. The upper field is often made smaller than the lower, so that as much ground as possible may be seen in the field of view. This system is known as the " invert," and is used in many field range-finders.
3. The whole field is erect with the exception of a small central rectangle in which the image is inverted. The advantage of this system is that the field of view is as large as that of a range-finder of the erect type, except that the part covered by the rectangle is missing. It is known as the " invert rectangle " and is used in many field range-finders, especially in foreign armies.
4. The whole field is erect with the exception of a narrow hori- zontal strip which passes right across its centre. The field in the strip may be either erect or inverted. This system, known as the " strip " system, is used in the British height- and range-finder.
In early range-finders the axis of the eye-piece was horizontal when targets in the horizontal plane were being viewed. It is now usually inclined downwards at angles of 45, 60, or even 90 for anti-aircraft work, so that the range-taker can observe from a more comfortable position. Eye-pieces can be focussed for individual observers, the two images of the target and the separating line coming to focus simultaneously. Coloured and neutral tinted glasses are useful in cutting out excessive glare, haze, etc. In some range-finders, the magnification of the eye-piece can be altered so as to obtain the best effect under various atmospheric conditions. Astigmatisers are sometimes used for drawing out a point of light or small object into long lines or bands. Coincidence, which without their use would be almost impossible to effect, can then easily be made. They consist of two negative cylindrical lenses with horizontal axes, one being placed at each end of the range-finder between the pentagonal and the objective.
Range-finders are provided with halving and coincidence adjustment heads, which, when turned slowly, move the optical systems mentioned above. Correct adjustment is of course essential for accurate work.
Accuracy of One-man Range-finders. The accuracy of the range-finder, other things being the same, depends upon its base length and magnification; but there are limits to the magnification which can be conveniently used. It is usually between 10 diameters (for the smaller range-finders) and 30 (for the largest). Under good conditions, two images can be aligned across a fine separating line, with an error of only a few seconds. There is little doubt that this degree of accuracy can be obtained under the best atmospheric conditions and when the target is stationary, as the mean result of several observations being taken as the range. If, however, the atmospheric condi- tions are bad and the target is moving rapidly, such accuracy cannot be expected.
The base lengths of range-finders used in the field usually vary between half a metre and two metres. The Barr and Stroud range-finder with a base of one metre, which is used for field artillery by the British and other armies, is typical.
German field coincidence range-finders, such as the Zeiss and Goerz, are used in a similar way to the Barr and Stroud, although their construction differs materially in details. Many of these were introduced to avoid infringements of earlier patents. The chief features of Zeiss coincidence range-finders are that they have only one eye-piece in which are seen a small rectangular inverted field in the centre of a large erect field and on the left of these a range scale. Coincidence is effected by revolving a working head which rotates two wedge-shaped prisms in opposite directions.
Stereoscopic Range-finders. The principle of the stereoscopic range-finder is entirely different. Stereoscopic rapge-finders have not found much favour in the British services; but they have been extensively used by the Germans. Speaking generally, a stereoscopic range-finder contains the elements of a stereoscopic telescope rigidly mounted in a tube. It is very similar in outward appearance to a coincidence range-finder with two eye-pieces. Objects viewed through a stereoscopic range-finder are seen to stand out in stereoscopic relief; and it is comparatively easy for the observer to judge their relative distances. The actual distance of a target is obtained with the assistance of one or more marks which are seen in stereoscopic relief in the field of view. By means of suitable optical arrangements the stereoscopic relief of either the objects in the field of view or of the mark can be varied until the target and mark appear to the observer to be the same distance away from him. The range of the target can then be read off a range-scale attached. The mark which is seen in stereoscopic relief, really consists of two similar marks which are photographed on glass diaphragms mounted in front of the eye-pieces of the range-finder. If the two marks are on the optical axes of the two halves of the range-finder, they will appear to the observer as one mark at an infinite distance. If the two marks on the diaphragms are made to approach one another, the resulting single mark will appear to come towards
