SIGNALS. 



51 



just below the stand for the instrument, for the observer. The two should 

 be separate, in order that the jarring incident to moving about on the plat- 

 form be not communicated to the instrument. Such a type of observing 

 tower is figured in Fig 1 . 4. 



FIG. 4.— si^n.il ami instrument support. • 



When sawed lumber is not obtainable, other material must be used. 

 In the Sierra Nevada of California, among the sugar-pine forests, a support 



