June 26, 1914. THE COLLIERY GUARDIAN. 1479 THE “EAGLE” THEODOLITE. Generally speaking, the prime requisites in a theodolite for mining work, apart from accuracy and other qualities looked for by surveyors are : (1) Rigid but light construction; (2) reduction in height and increased portability; and (3) ability to take readings on any vertical line between nadir and zenith by means of one main telescope. These are the points to which Mr. George Eagle has devoted his attention mainly in a new theodolite devised by him, and made by Messrs. A. G. Thornton Limited, of the Paragon Works, King-street West, Manchester. With the usual form of theodolite it has not been possible to take sights downwards within about 40 degs. of the vertical. The vertical range of this form is shown in diagram No. 1 (fig. 2). Mr. W. Davis Haskoll, engineer, designed a theodolite with a hollow centre, through which sights could be taken downwards verti- cally or within about 5 degs. of the vertical. There remained, however, an arc of about 35 degs. through which sights could not be taken. The vertical range of these hollow centre type of theodolites is shown in diagram No. 2 (fig. 2). For situations in which sights must be taken downwards within 40 degs. of the vertical various forms of theodolites with eccentrically mounted auxiliary side or top telescopes have been designed. In almost every one of these situations only one sight of extreme dip has been required from any given station, and to meet such a simple requirement the “Eagle” theodolite has been designed. In this instrument a gap has been cut in the horizontal plates of the instrument between the hollow centre and the graduated horizontal circle. The tripod of the theo- dolite may be so set up at a station that in one required horizontal direction from that station (or within about Fig. 1.—The “ Eagle ” Patent Theodolite. 5 degs. of that direction) a sight may be taken at any angle from the vertical without the use of an auxiliary telescope. The vertical range of the gap type of theo- dolite (for a horizontal range of about 10 degs.) is shown in diagram No. 3 (fig. 2). In order to obtain a view through the horizontal plates a gap has been cut from the hollow centre to the circum- ference, except through the graduated circle and cone centres, which could not be cut away without destroying the instrument. These parts which could not be cut away have been arranged to form parts of two cones with the common apex of the two cones at the centre of the transit axis, where the horizontal and vertical axis intersect, with the result that viewed from this inter- section these parts appear only as two narrow bars across the gap. As these bars are so near the object glass they are not visible through the telescope, and do not interfere with or spoil the definition. They cut off a certain amount of light which is only just noticeable, and which has been allowed for by making the object glass of slightly larger diameter than usual. The general appearance of the 5 in. “Eagle” 'theo- dolite is shown in firr. 1. From this it will be seen that the whole instrument is very compact. The various milled heads of the focussing, pinion, adjusting, and tangent screws have been brought out well away from the instrument to ensure plenty of finger room. In a new type of telescope the objective consists of a positive and a negative element. The distance between the two elements decides the focus of the combination. In adjusting the telescope this distance can be varied until the focus of the combination is a given multiple of the distance between the engraved lines on the diaphragm. This type of telescope can be adjusted and guaranteed accurate as easily when fitted with an engraved glass diaphragm as when fitted with any other form of diaphragm. In the telescope described the combined focus is 9 in. and the stadia 9/100 in. Obviously it is easier to adjust to say l/1000th part of 9 in. than to l/1000th part of 9/100th part of an inch. The introduction of the above-mentioned negative lens has had the effect of magnifying the image at the dia- phragm before it has to be again magnified by the eye- piece. In the telescope now described this preliminary magnification is two diameters. This gives an image magnified twice as much as the engraved lines of the diaphragm are magnified and the lines appear fine. The introduction of the above-mentioned negative lens has also had the effect of obtaining a long focus in a short telescope. In the telescope now described the combined focus equivalent to an objective of 9 in. focus is obtained in a telescope tube only 5| in. long. This shortening of the telescope tube, without using a short focus objective has allowed the standards to be made shorter than usual, and has also had a larger share in Fig. 2. Fig. 3.—Diagrammatic View of Theodolite and Telescope. S3 ■ Ml i making it possible to produce a low and compact instru- ment without loss of focal length in the telescope. Special provision has been made for the cleaning (by the surveyor) of the internal lens. The diaphragm and eyepiece may be first unscrewed, then an internal tube is also unscrewed, and the internal lens may then be removed for cleaning. All the screws are marked with a centre mark to show where they are screwed home. Their construction is convenient also for the fitting of an adjusted spare or alternative diaphragm as often required by Colonial surveyors. In the telescope now described the stadia distance is measured from a point in front of the object glass, and a constant must be added to get the distance from the centre of the instrument. This constant will be found noted inside the lid of the instrument box. The two bars across the gap that could not be avoided, and which have been mentioned above, have the effect of reducing the aperture of the object glass when the telescope is directed downwards at certain angles. In the telescope the object glass has a full aperture of one- eighth of the combined focus of the lenses. In the two worst positions of partial eclipse the working aperture is one-twelfth of the focus. The telescope has a power of 13, but higher power eyepieces could be fitted if desired. A diagonal eyepiece is also fitted. In order to illuminate the diaphragm with any safety or other lamp which the surveyor is obliged to use, a small reflector has been fitted in the cap of the object glass. As this cap can be turned the reflector may be turned into any convenient position to suit various situ- ations. A lamp or light of any kind held opposite this reflector will illuminate the diaphram. Fig. 3 is a section through the instrument to show the general construction. The centre, being hollow, must of necessity be of larger diameter than usual, and is, therefore, rather more difficult to make, but this arrangement gives larger wearing surfaces, and (when once ground in) a longer life of accuracy to the instru- ment. The large diameter of the hollow centre is also stiffer and stronger than the solid centre, weight for weight. In this instrument the horizontal plate which carries the standard turns directly on the main cone centre, which is screwed to the tribrach. The hori- zontal circle is 5 in. in diameter, and two opposite verniers give readings to a minute. The use of a short telescope has allowed the height of the standards to be less than usual. The two stan- dards are in one casting, and the base of attachment to the horizontal plate is equal to their height, a construc- tion which makes the connection between the horizontal and vertical very rigid. The standards are triangular parts of the surface of a cone with a spreading base, and this slight curve in cross section adds greatly to their rigidity. A new solid construction has been adopted, which avoids the use of locking plates and their unsatisfactory fit after much use. The easting which forms the top of the tripod has a truly circular hole drilled in each of its three solid arms. The ball of the adjusting screw which fits into this drilled hole is split, and the lower half of the ball is pressed down by a pressure screw inside the adjusting screw. If at any time the ball wears loosely in the drilled hole the ball may be expanded by means of this inner pressure screw. The two halves of the ball are dowelled together to avoid any play which would tend to release the pressure. If the three legs of the tripod are taken away from the head of the tripod, three points will be found under the tripod head, on which the instrument will stand if desired on wall or timber. KNIGHTHOOD FOR THE CHIEF INSPECTOR. The conferment of a knighthood upon Mr. Richard Augustine Studdert Redmayne, H.M. Chief Inspector of Mines, is a matter of no little interest to mining engineers. Mr. Redmayne was born on July 22, 1865, at South Dene, Gateshead-upon-Tyne. He was edu- cated privately, and then passed through the Durham College of Physical Science. In 1883 he entered upon his apprenticeship at the Hetton Collieries, gaining his certificate in 1886. During 1891-3 he was in Natal, and in the latter year was appointed resident manager of the Seaton Delaval Collieries. This post he vacated in 1902 to take up the professorship of mining at Birming- ham University, which he filled until 1908, when he was called upon to undertake missions for the Home Office, shortly afterwards being appointed to the post [Photo by Elliott and Fry. of Chief Inspector of Mines, and head of the newly- created Mining Department at the Home Office. Since that time Mr. Redmayne has acted on every committee or commission engaged in the examination of problems relating to coal mining in this country, an enumeration of which it is unnecessary to give here. Mr. Red- mayne’s literary activities have been considerable, being by no means confined to the numerous official reports that have been issued above his signature; he is the author of Modern Practice in Mining, which, we believe, is still incomplete; joint author, with Mr. F. H. Bulman, of Colliery Working and Management; and for some years edited the Colliery Manager’s Pocket Book. It may be added that the Chief Inspector is related by marriage to the Prime Minister. South Staffordshire ana Warwickshire Institute of Mining Engineers.—The next general meeting will be held at the University, Edmund-street, Birmingham, on Monday after- noon, June 29, at 3 p.m. The following paper : “ An Instrument for the Detection of Firedamp in Mines,” will be read by Mr. F, J, Turquand.