Illumination of Cross- Wires 



For Mining and Tunnel Transit*. 



In our instruments this sometimes consists of a hole drilled through the transverse axis 

 of tL telescope and closed at either end with small glass plates, to prevent dust entering 

 the telescope Then in the center of the telescope is placed a small adjustable reflector, 

 by mean lot which the cross-wires can he very readily illuminated in the mine or tunnel by 

 the"eriecUon of the light of a lamp held in the hand or placed on a sma 11 table, which is 

 attached to the standard. This lamp is provided with a ground ens. While this method 

 ?s satisfactory, still the small mirror has to be placed at a point where the cone of rays 

 from the object glass is small and consequently it cuts off much of the best part of the 

 liffht not to speak of the weight of the lamp and table at the side of the standard and the 

 heat 'imparted. This method is not thought to be of as good repute as it was formerly. 

 In -ill cases we would advise the use of our reflector, placed in front of the object glass in 

 a tube like the sun-shade. This arrangement gives perfect satisfaction. This may be used 

 in connection with an ordinary lamp or with the pocket electric lamp. 



Arrangement for Offsetting at Right Angles. 



A perfect line of sight can be had at right angles to the telescope by perforating the 

 telescope axis and covering the ends with glass plates as described in the preceding 

 paragraph. By simply sighting through the axis, offsets may be conveniently estab- 

 lished without disturbing either clamp or telescope when the eye is brought close to 

 the instrument ; its application is, however, limited to even ground. To use it on an 

 uneven ground it is necessary to place the eye at a distance of twelve or fifteen inches 

 from the instrument. The head should then be moved until the eye is in line with the 

 openings of the transverse axis. An offset can then be aligned irrespective of the height 

 of the instrument. 



Quick Leveling Attachment. 



This we can apply to any of our Mining and Mountain Transits and Leveling 

 Instruments. It adds about 1 Ib. to the weight and $8.00 to the cost of an instru- 

 ment. 



Protection to the Object-Slide, &c. 



A rain and dust guard for the object-slide is now furnished with all of our 

 telescopes, and to insure smooth working of the object slide and telescope tube 

 both are made of a non-friction metal. The graduation of the horizontal circle, 

 the centers and such other important parts that are liable to injury by the action 

 of dust and water in the field-use of an instrument, are entirely protected. 



General Construction. 



In regard to the general construction of our instruments, the dead weight is 

 removed wherever it is shown to be not essential to the stiffness of the instrument ; 

 but we have at the same time strengthened the parts most likely to be injured by 

 an accident or fall. Thus the base of the standards, the vernier plate and circle, the 

 parallel plates for leveling screws, the telescope axis, the flanges of centers, cross-bar 

 of level, etc., are made especially rigid and provided with ribs. Instead of finishing 

 the smaller pieces of an instrument separately and then joining them with small 

 screws, or solder, each screw or joint being a weak place in an instrument, we have 

 adopted the opposite principle, (at an increased expense to us,) and aim to unite as 

 many pieces as possible in a single casting, which casting, by means of ribs is made 

 as light as consistent with strength. 



We also call attention to the exceptionally hard bell-metal and phosphor bronze 

 used for our centers and telescope axis, which are long and unyielding, and the 

 remaining parts are of a composition metal, which is itself harder than hammered 

 brass, or red composition, used ordinarily for centers, etc. It is more difficult to 

 work, but we avoid the objectionable softer brass in its use. Experience has 

 proven that soft, or hammered yellow brass is unfit for a good field or astronomical 

 instrument, since it is more liable to fretting and yielding generally, and in the 

 hammered state its unequal expansion and contraction ai different temperatures 

 may be so marked as to impair the reliability of the adjustments. 



Aluminum bronze containing 90% copper, is also extensively applied in our instru- 

 ments on account of its great tensile strength. 



Almuminmn alloyed with small percentages of silver or copper must be used with 

 caution on account of its softness. (See Aluminum for Instruments of Precision, 

 page 27.) 



