4 SEC. 1. - ARITHMETIC. 



14. Pocket Calculator, arranged by Major-General A. De 

 Lisle, R.E., for the use of engineers. Elliott Brothers. 



This slide rule is useful for finding the weight of various materials, with the 

 help of the small tables on the back, for checking bills of quantities, and for 

 all approximate calculations required in engineering practice. The slides 

 are: 



On Face. 



On Stock A. The ordinary logarithmic line. 



I. The same inverted. 

 On Slides Upper I. Inverted line. 



D. Line of squares. 

 Lower B. Ordinary logarithmic lines. 



c- n > Trigonometric lines. 



Special Marks 



M. Modulus of logs, to find prop, parts of logs. 

 A. Eeciprocal of M. to find hyperbolic logs. 

 S" To find length of arcs, &c. , 

 R' Radius for minutes. 

 R Radius for seconds. 



On Sack. 



On Stock D. Line of squares. 



On Slide E. Line of cubes read with D on line off powers read with A. 

 F. Line off powers read with D, or of -| powers read with A. 



Tables and useful Numbers. 



Line E with A gives variation in depth of water running over weir due to 

 alteration of length of weir. Neville's Hydraulics, page 22. 3rd edition. 



A _ 143 = ^ __ 

 E _ 220 = / ___ 60 = 1' 

 A G = d 



Line F with D assists in finding the dimensions of a pipe or channel, with 

 a given hydraulic inclination to discharge a given quantity from the calculated 

 discharge of a pipe or channel of known dimensions and the same incli- 

 nation. Thus, if a pipe 4" diameter discharge 15 cubic feet per minute, what 

 diameter will discharge 33 cubic feet. Neville's Hydraulics, page 245. 



D __ 

 F _ 15 = D _ 33 = D' 

 D 4 = d 5.48=d' 



The two slides on the face working together solve the following equations : 

 ab abc abed 



15. Slide Rule, of boxwood, with double slide. 



Renaud- Tachet, Paris. 



16. Routledge's Original Engineers' Slide Rule and 



manuscript book of instructions for using it. 



Lent from the Patent Office Museum by the Commissioners 

 of Patents. 



