harmony of proportion, yet I should certainly doubt the adequacy of its opti- 

 cal power for long lines; it reads by four verniers instead of three, involving 

 more labor, and less reading points on the circle; whilst the observer must 

 be placed in a constrained position because the horizontal plane ofthe ;ele- 

 scope is only about two inches above the reading microscopes. Moreover, the 

 circle (instead of the whole instrument) is changed for new positions and 

 clamped by three screws in each position. Should the surface planes of con- 

 taot be warped, this clamping would warp the circle in each new position and 

 thereby introduce error. This method was devised about 20 years since, and 

 soon abandoned; it is now the fashion. 



In the evident desire to obtain compactness and simplicity, the instru- 

 ment is not adapted to the observing of azimuths by means of a close cir- 

 cumpolar star, because the telescope cannot be ele/ated. Instead, the transit 

 instrument w isi replace the theodolite for that purpose, whereby the possibility 

 of error is introduced in occupying the identical station; and even it this be 

 granted, the labor is increased and extra time consumed. 



Fashions prevail among instrument makers and observers just as we find 

 a change of opinion upon the question of refractors and reflectors. At one time 

 it seemed as it the prismatic telescope was to carry everything before it, and 

 I find many manufacturers and observers yet strongly in favor of that form. 

 It certainly has the dec'ded advantage of comfort to the observer; but from 

 personal experience, and from conferring with such observers as Plantimour, 

 it seems that the system ncessarily in/olves "flexure" or deformation of the 

 prism, notwithstanding the njmerous and ingenious efforts made to secure it 

 properly in position. Of course some manufacturers insist that their special 

 methods of securing the prisms are infallible; but the observer is the final 

 jtt^ge of their failures. In the highest character of wo ^k I should certainly not 

 use them; whilst for the secondary works it seems hardly necessary to increase 

 the number and Intricacy of the parts. 



A prevailing fashion at present is to introduce reversing apparatus and 

 counterpoises, even in theodolites with circles of eight inches in diameter. 

 This is as complete a wandering from simplicity as can well be imagined, and 

 must certainly lead to grave errors. It is well known that by moving a tele- 

 scope in altitude by means of the usual slow-motion screw, the tendency is to 

 raise the transit axis pivots, but as the weight of the telescope is too great to be 

 lifted clear of the Y's, the pivot is moved up one side of the sloping Y, and 

 the telescope thereby changed in azimuth. Now, if the weight of the telescope 

 be counterpoised by springs, the pivot is lifted still higher and the resulting 

 change in azimuth becomes greater. Not only that, but the intricacy of the 

 adjustment thereby introduced, conflicts very much with the bearings of the 

 vertical axis. I saw no form of reversing, that should be applied to any first- 

 class theodolite, or to any theodolite which might be used at a distance from 

 the workshop of a skilled mechanic. The same amount of labor otherwise 

 expended upon the same instrument, would largely increase its value for honest 

 work. This form, as well as the prism telescope, must however be demanded 

 by observers or the makers would hardly continue their manufacture. 



Another fashion that seems to prevail is the use of microscope micrometers 

 upon small theodolites of eight inches diameter, and even in some cases of only 

 six inches. These microscope micrometers read the circle to one or to two 

 seconds; but in every such case the telescopic power and the transit axis level 

 were vastly inferior to such delicacy, and therefore the contradiction existed 

 that the instrument maker expected the observer to measure what he could not 

 see. In fact, I think it may be safely asserted as a rule that the telescopic power 

 of all the instruments examined was inferior to the other parts. 



And still another fashion is in the use of the universal or Altazimuth in- 

 strument. The combination of two or more instruments for differeut purposes 

 into one instrument for all the required purposes is difficult and doubtful even 

 in machines of industry; but when every new piece and movement introduces 

 a fresh source of error into a delicate instrument where the constant-study 

 should be really to decrease them, the combination must be clearly shown not 



