R. S. Woodward — Iced Bar Base Apparatus. 37 



For measuring grade angles a sector reading by two oppo- 

 site verniers to 10" is attached to one side of the trough near 

 its middle point. Thus arranged this sector has great sta- 

 bility. 



The ice load and ice crusher. — When the apparatus is in use 

 the Y- trough is completely filled with pulverized ice, the 

 upper surface of which is rounded to about the height shown 

 by the curve B H F in the diagram. The amount of ice 

 required for this purpose is about 40 kilograms, or 8 kilo- 

 grams per meter of the bar's length. The ice, by reason of 

 its weight and the sloping sides of the trough, is kept in close 

 contact with the bar. This is especially the case when the 

 apparatus is in use, for it is then trundled along on its cars 

 with sufficient jarring to overcome any tendency of the ice to 

 pack. For covering the ends of the bar a small quantity of 

 ice is cut with a jack plane. Ice thus cut, like wet snow, packs 

 well and permits making a small conical hole through it to the 

 graduation plugs. 



A very essential auxiliary to the use of the apparatus is an 

 ice crusher to pulverize the ice. The machine used is a modi- 

 fication of the Creasey ice breaker manufactured at Phila- 

 delphia, Pa. It is a small light hand machine which, as 

 modified, does its work very satisfactorily. With it 40 kilo- 

 grams of ice may be pulverized in ten minutes or less. The 

 particles of crushed ice vary in size from the smallest visible 

 up to the bulk of a cubic centimeter ; and this gradation in 

 size appears to be advantageous as compared with uniformly 

 finer particles like those of snow, since there is less liability 

 of regelation and packing. 



The cars and portable track. — The Y-trough is mounted on 

 two cars, the saddles or bolsters of which are attached to the 

 trough 40 cm from either end. Each saddle is attached rigidly 

 to the trough above and to a jack screw below. The jack 

 screw is attached to a slide rest which is connected rigidly 

 with the base of the car. The slide rests are provided with 

 screws to give slow motions in the direction of the trough's 

 length and transverse to its length. 



The jack screw cylinders have right and left handed threads 

 at their respective ends and are turned by a short capstan bar. 

 They give thus the rapid vertical motion to the trough essen- 

 tial in bringing the bar quickly to focus under the micro- 

 scopes which define its position. 



The cars have each three wheels and run on a portable 

 track whose width is 30 cm . Three sections of this track, each 

 5 m long, are provided ; and each section is carried forward as 

 the cars are rolled along during the measurement of a line. 

 It thus appears that instead of lifting up and carrying forward 



