334 SURVEY OF THE COAST 



mentioned a little inwards, it may be disengaged from the pin 

 in the piece q, which holds it in its position. Tlien the axis 

 of the telescope can be lifted out of its supports, and the 

 whole upper part, which serves to measure vertical angles, 

 can be taken off, and placed in an inverted position for the 

 verification of the line of collimation of the telescope, tliough 

 it can not serve in this inverted position for tiie measurement 

 of vertical angles. 



The verification telescope below the instrument is exactly 

 similar to the upper, and can, if desired, be used in its place. 

 It hangs in hooks x^ x, one of which hangs from one of the 

 legs, and the other from an arm of the stand part of the in- 

 strument, purposely intended for it. It is pointed in the 

 same manner as that of the two-feet theodolite, by an ar- 

 rangement w of three sliding tubes, and a screw presenting 

 its head to the upper part of the telescope tube at the eye 

 end, which is pressed upwards to it by the overpoise of the 

 object end. 



To ease the first approximate levelling of the instrument, 

 there are two small levels k, k, about two inches and a half 

 long, and half an inch in diameter, placed at right angles to 

 each other, at the side of the socket of the axis, between the 

 two columns, on the side opposite to the vernier marked A, 

 which in the figure show only a little between the axis and 

 the columns. 



The elevation of the upper telescope above the horizontal 

 circle increases the facility of observing very high altitudes. 

 The eye end passes through the nadir above the piece f, 

 crossing the top of the vertical axis. The whole instrument 

 is about thirty-two indies high, and the base of it through 

 the truncated cones is a circle of about nineteen inches in 

 diameter. It is therefore well proportioned for stability, par- 

 ticularly as the upper parts are not heavy. 



In my original plan several of the arrangements were dif- 

 ferent. They were executed with great success in another 

 instrument ; and every artist or practical experienced ob- 

 server will of course vary the disposition of many of the parts 



