140 



Plane Table. 



This instrument, made by us now in one size only, is designed to fill a want where 

 A high class of work in Topography is required. 



Jn order to obtain great rigidity and strength the bearing surface of the lower 

 motion has a diameter of eight inches, the board rests on arms lyini: in a circle twelve 

 inches in diameter and the tripod is of corresponding size. To be still portable all the 

 essential parts are built on the skeleton plan to be light and stiff as shown in cut. To 

 avoid a loosening of the leveling screw-fastenings, so often experienced where they are 

 fitted into tripod heads made of wood, we make this head of composition brass, same as 

 the other parts. To reduce this weight by the use of aluminum, see pages 122, \-i\\. 

 The board is 24 x 28 inches. The alidade is 22 inches long and Is provided with a 16- 

 inch inverting telescope having an aperture If inches and a power of 35 diameters. It 

 has stadia wires, a vertical arc reading to minutes, graduated on solid silver, and a sen- 

 sitive striding level. Two fixed levels are mounted on the rul^r. The latter is so ar- 

 ranged that lines can be ruled in the vertical plane of the line of collimation, if desired. 

 For adjusting the line of collimation the telescope can be revolved 180 on its longi- 

 tudinal axis. Materials and workmanship are of the best. The alidade is bronzed 

 Mid lacquered in our customary manner, but the tripod head and lower motion are 

 neatly japanned. 



Weight of Alidade with brass ruler, Gibs, 



' Lower motion, 11 



" Tripod, about 18 



" Board 8 



" Alidade and accessories in mahogany box, . " 15 



" Lower motion in mahogany box, " 18 



" Board in pine box, " +:} 



Gross weight of instrument packed in four boxes ready for shipment, " 110 " 

 Price of Plane Table, complete as above, including board, detached 

 compass, screwdriver, clamps, reading glass, plumb bob, etc. , in three boxes, $3OO.OO 



NOTE. We have sometimes been asked to furnish a larger base to increase the steadiness of larger 

 boards. We do not desire to make this, since we are fully confident that our standard base, as above described, 

 is amply stiff. We are prepared, however, to make a base with arms, lying in a circle, 16 inches in diameter, 

 should a much larger board be required. The increase in weight will be about 10 Ibs. Price, extra, $25 00. 



If two tangent screws are desired for this larger lower motion, the extra cost of instrument will be 40.00. 



For use with such a large boat d we are also prepared to furnish an alidade, 28 inches long. 



Price, extra, $10.00. 



Price of Alidade, complete as above, including striding level, detachable 

 compass, clamps, etc., in mahogany box, but without board, lower motion and tripod. 



$1*OO.OO 



To meet a want where greater portability and lightness are thought to be more 

 advantageous than greater rigidity and consequent accuracy, we are prepared to 

 furnish in place of the above described lower motion of the Plane Table (shown in 

 the accompanying cut) one of the Johnson type and character. A description of 

 this may be omitted here, since it is described in any of thr modern i'xt-Uo<>U> <>i\ 

 Plan*- Table Work. Suffice it to say that this motion is operated in a manner simi- 

 lar to that described under our Quick Leveling Attachment (see pages 3l and 1-JO i 

 of which it is an inverted adaptation, but is of greater size, range and steadiness. 



This movement., with legs all complete, weighs only from 9 to 10 Ibs. 



Price of Johnson's Improved Plane Table Movement, mounted <> l,ir<ic 



$4r.no 



Price of Plane Table Drawing Board, in pirn icood box, . . $1 5.OO 



