and Traverse IVorker. 4S3 



to be found on the slide, and dep. on the limb ; and the same 

 is to be obsei'ved when the diff. of lat. is less than the dep. : 

 that is, set off the diff. of lat. on the slide, and the dep. on the 

 limb, when these are given to find course and dist. ; and the 

 angle of the course thus produced will be found on the arch, 

 and must be read off from right to left, as it will be more than 

 45 degrees. For instance, let the diff. of lat. be 60', and the 

 dep. 42', to find course and dist., shift the slide to 60 on the 

 divided limb, (the diff. of lat.,) and move round the index till 

 it cuts 42' on the slide, it being the dep. On the arch is the 

 course, 34° 58', and on the index is 73'*2, nearly the dist., cut 

 by the division 42 the dep. Now, without altering the position 

 of the sides of the triangle, admit that the diff. of lat. be 42', 

 and the dep. 60', to find course and dist., it will be quite clear 

 that the diff. of lat. now is on the slide, and the dep. on the 

 limb; and the course corresponding to this diff. of lat. and 

 dep. is 55° 2', with dist. as before 73''2. 



Fourth. To find or set off any required number on the sides 

 of the triangle on the common scale, No. 10 to 100 on the 

 limb and index, and to 75 on the slide. Required that the 

 slide should be placed to 532 on the diff. of lat. or limb. First 

 find 53 ; then take the first subdivision next to this last, is 3%; 

 to this 2}lace the edge of the slide, and you will then have on 

 the diff. of lat. side 53*2, the number required. But this num- 

 ber may be called 53'20, thus bringing out the result to two 

 decimal figures, which is equal in accuracy to the table of 

 logarithms, only with this great advantage, that the results are 

 had by the instrument tenfold easier and quicker. The same 

 numbers may also be counted 532. Now the large scale is 

 numbered 1 to 5 on the two longest sides, and 1 to 3 on the 

 slide. This scale is convenient when working for the mei'i- 

 dional diff. of lat. as it frequently happens to run up to thou- 

 sands. Example : — Required the slide to be placed to 3530 

 on the divided limb. Look for 3 on the large scale on the 

 limb ; then take 5 of the longer divisions above, and it will be 

 500, and the next three subdivisions on the edge, will be 30. 

 To this bring the slide's knife edge, and that will represent 

 3530 as required. With the slide thus set, let it also be re- 

 quired to turn the index on the division of 2450 on the slide. 

 Find 2 on the large scale on the slide, then the four longer 

 divisions to the right hand will be 400, and the next longer 

 division which is cut up to the second line will be 50. To this 

 last, turn the index's divided edge, and you will have 2450, 

 the number required on the slide, producing an angle of 

 34° 45' on the arch, with a dist. of 4293 on tl)e index. If 

 short boards are made, as 2 to 6 miles, which often happens 



N. S. Vol. 11. No. 66. June ] 832. 3 K in 



