36 M. S. Woodward — Iced Bar Base Apparatus. 



when the lines on these plugs are in one straight line. The 

 means of securing these two adjustments are described below.* 



The Y-Trough. — The most important and distinctive part 

 of this apparatus is the trough which supports the bar, keeps 

 it aligned, and carries the ice load essential to control the bar's 

 temperature. This trough is called the Y-trough by reason 

 of the resemblance of its cross-section to the letter Y. The 

 drawing shows a cross-section of this trough. It is made of 

 two steel plates 514 m long 25-5 cm wide and 3 mm thick. They 

 are bent to the angle BCD of the figure and are riveted 

 together as shown at E, thus making the angle of the trough 

 BCF= 60°. The bar, shown in cross-section at A, is sup- 

 ported at every half meter of its length by saddles, one of 

 which is shown in the figure. These saddles are rigidly at- 

 tached to the sides of the trough by screws at S, S. Each 

 saddle carries one vertical and two lateral adjusting screws as 

 shown at V, L, L/. These screws serve to fix the alignment of 

 the bar. The lateral adjusting screws of the saddles at the 

 ends of the bar are of the same height, which is equal to that 

 of the lower screw L' of the diagram. The lateral adjusting 

 screws of the intermediate saddles on either side of the bar are 

 alternately high and low. The object of this disposition is 

 two-fold, to wit : 1st, to prevent pinching the bar, which 

 might more readily occur if the lateral screws were all oppo- 

 site to one another ; 2d, to afford means of rotating the bar 

 slightly about its longitudinal axis, so that for a fixed and 

 nearly vertical position of the trough the graduated surfaces 

 of the bar may be made horizontal. The vertical adjusting- 

 screws of the saddles project, as shown in the diagram, below 

 the vertex of the trough, and their capstan heads are accessi- 

 ble through slots cut in the web of the trough. These slots 

 serve also as drainage-ways for the melted ice. To prevent 

 circulation of air through them they are stuffed with cotton 

 batting, through which the water percolates freely. The ends 

 of the trough are closed with wooden V-shaped blocks. 



The trough is very rigid in all directions and especially so 

 with respect to vertical stresses. It weighs 82 kilograms 

 exclusive of the bar and ice load. The whole trough is cov- 

 ered by a closely fitting jacket of heavy white cotton felt, 

 which protects the trough and ice load alike from direct 

 radiation. 



* The form of bar described is evidently not the best form. Theory and experi- 

 ence indicate that a bar having a T-shaped cross section with metric subdivisions 

 on its neutral surface would best meet the requirements However, the question 

 which presented itself in planning the apparatus was not what is the best form of 

 bar, but what is the most economical form possessing the requisite properties. 



