75 



These devices are being more and more perfected, and will be protected by letters 

 patent, and Messrs. C. L. Berger & Sons make and sell them exclusively. 



2. Remarks. Certain precautions are necessary in the use of this method 

 of finding the true direction of a line as well as in any other. It is not wise to 

 observe the sun, read the circles, note down the readings and leave the instrument 

 standing there while making the reductions. It will get out of place in some way, 

 very likely. Therefore, as soon as the observation is completed and the readings 

 of the circles noted, set the line of sight on some fixed point and read the plate 

 again, noting this reading. Of course the two plate readings will give the horizon- 

 tal angle from the sun to the line. This will enable the observer, after finding the 

 direction of the line of sight when set on the sun, to readily ascertain its direction 

 as set on the fixed point referred to, thus determining the direction of the line from 

 the point over which the instrument is set to the fixed point. This line may be 

 chosen before beginning the observation, and become the reference line for the 

 work in hand. 



3. Remarks. For the purposes of reduction the process by equations is 

 used instead of one by rules. The introduction of symbols and signs is a much 

 simpler matter than many suppose. It is nothing but this. We agree that a char- 

 acter of some sort or other shall represent a certain thing and nothing else. 

 Whenever this character occurs, therefore, it simply means the thing we have set 

 it for. That is all there is of symbolical representation. These very words here 

 printed are all symbols. The method is universal. We here, as elsewhere in 

 algebraic processes, make a special application of it. The rules for a case of this 

 kind would be very cumbersome and give the user far more trouble than will be 

 necessary for mastering the few equations given below. The record of the pro- 

 cesses is hereby reduced to a few lines, and one has not to go searching through i\ 

 page for a point here and there, but places his eye at once upon what he wants, 

 where all will be found in a compact form. Of course one needs to read each word 

 and each sign. Nothing must be slurred over or missed. The record as set forth 

 below is exact, complete and reliable. 



4. Remarks. All computations should be thoroughly checked, and check 

 equations and devices are given. These should always be applied, without fail, as 

 no one can implicitly trust a computation by a single process, unrepeated, even if 

 simple. No one should who is a surveyor of engineer. Several checks are given. 

 One used is sufficient, usually. If one distrusts the check because it shows thu 

 work to be wrong, it may be of some satisfaction to use another or more than one. 



5. Remarks. The directions prepared below are intended for use, word by 

 word, and step by step. It is hoped that they will prove in convenient form foV 

 use as a chart to direct the efforts of the observer in his first use of these attach- 

 ments and this method. Therefore, it is thought that one may safely do as told, 

 trusting the next step to the next statement. They have been prepared with this 

 view. 



6. Using the Screen. 



a. Directions. Set the instrument so the sun can shine in at the object end 

 of the telescope, and directly through it. Run put the eye-piece and adjust the 

 screen behind it, by its sliding arm, so that a distinct image of the cross-wires can 

 be seen on the screen within the lighted spot made by the shining sun, as shown 

 in fig. 2. Set the object glass so as to clearly define the image of the sun on the 

 screen. Repeat these trials, and adjust the parts of the telescope and screen so 

 that the clearest image of both the cross-wires and the sun will be obtained that 

 the telescope will give. Mark the slide on the arm of the screen and the eye-piece, 

 so they can be easily set thereafter for an observation. 



6. Remarks. The eye-piece, when all is in exact position, will be found to 

 be considerably farther out than for an ordinary sight. The marking of the sliding 

 arm and eye-piece will save time in the future. These trials, when made with a 

 new apparatus, should be conducted at leisure and with extra care, for the purpose 

 of fitting the apparatus carefully to the telescope. A few trials may be needed at 

 first in order to accustom the observer to recognize the best definition of the images. 



This solar screen is especially adapted to the ordinary surveyors' and engineers* 

 transit telescopes, with erecting eye-pieces. It is not adapted to be used with invert- 



