147 



No.lc, Style o. 



C. L,. Berber & Sons' Double Opposite Vernier Attachment to 



transits provided with a 5-iiich full vertical circle. 



Price, extra, $2O.OO 



NOTE. For most work with the Engineer's transit it is not important to read the vertical angles closet 

 than minutes, and by estimation to 30", and the ordinary vertical arcs and circles of our construction, as illus- 

 trated in the preceding instruments, give the fullest satisfaction in this respect. There are, however, some 

 few cases where it may be desirable to eliminate errors and excentricities in the graduation and verniers of the 

 vertical circle in the same manner as in the horizontal graduation by reading two opposite verniers, and the 

 construction illustrated above has been designed to meet this want. As the vertical circle cannot be turned inde- 

 pendently on its axis, as in repeating circles, the telescope must be reversed, when a repetition of the angle is 

 desired. The mean of the two readings is then accepted as the true result. 



In the above illustration the frame in front of the vertical circle carries two opposite verniers reading to 

 minutes. The verniers are double, so that angles of elevation and depression can be read with ease and dis- 

 patch. For ordinary work the vertical angles may be read only from one vernier. The frame is fitted to the hori- 

 zontal axis of revolution, and is circular in order to protect the graduation of the vertical circle from injury. 



Two opposing capstan-headed screws, working against a projecting stud on the standard, are provided, to 

 adjust the zero-points of the verniers to coincide with those of the vertical circle, after the instrument has been 

 leveled up and the telescope placed in a truly horziontal position, and when adjusted so that there is no loosenes? 

 between the stud and the capstan-headed screws the vernier frame maintains a fixed position, while the tele- 

 scope and circle are moved in altitude. This device can be attached to transits provided with a 5-inch fuf 

 vertical circle in new instruments only when so ordered. 



The Tachymeter, or Uniyersal Surveying Instrument. 



On the following pages, descriptive of the Complete Engineer's and Surveyor's Transits, No. 1 c Style f. 

 to transit No. 1 A inclusive, the name Tachymeter has been used. The want of a specific name for the complete 

 form of the engineer's and surveyor's transit has long been felt. The term "transit" originally borrowed from 

 a <! tronomy to designate an instrument whose telescope can traverse the vertical plane, is not 'sufficiently com- 

 prehensive to describe an instrument in which the vertical motion of the telescope is no longer its most important 

 characteristic. An instrument having a level on its telescope, a vertical arc or circle, and stadia wires, is 

 adapted to the rapid location of points in a survey, since it is capable of measuring the three co-ordinates of a 

 point in space, namely, the angular co-ordinates of azimuth and altitude, and the radius vector, or distance. The 



The compass and gradienter are auxiliaries in the measurement of angles, and an instrument having them, in 

 addition to the essential features mentioned above, is more perfectly adapted for tackymetric work. We fed 

 that we need make no apology for introducing these brief but expressive terms into our catalogue, and we ven- 

 ture to hope that they may co'me into as general use in this country as they have in Europe, and replace the in- 

 convenient phrases now employed to describe these instruments and methods. 



