2 



opened to me, and Ml and free explanations made to my inquiries. It would 

 therefore be unjust to these manufacturers to severely criticise in public the 

 character or even the minor defects of their instruments, or to make known the 

 methods of their processes. These I received for the benefit of the Govern- 

 ment, and whenever I mention any names here, it will be to commend their 

 work; although many are officially commended that are not now referred to. 



In previous experiments upon the larger and finer instruments, I have dis- 

 covered errors of graduation and flexure of parts much greater than I had 

 any reason to suspect; and I believe much greater and more serious than the 

 makers had thought possible. This latter is the more readily understood 

 when we reflect how few mechanicians are actually observers; and that it 

 really requires long practice for the most skilled observer combined with 

 fair mechanical instincts to discover and measure the minute and conflicting er- 

 rors which are resultants of diflferent infinitesimal, and perhaps unsuspected 

 causes. As a rule, the observer makes his measures upon objects subject to many 

 extraneous and disturbing causes, and whenever unsatisfactory results are ob- 

 tained, he is very apt to attribute them to the unfavorable conditions of the 

 atmosphere or to his own condition and temperament at the time; generally 

 overlooking the fact that the instrument maker was quite as liable as himself lo 

 errors of judgment in the proportions and workmanship of the instrument used. 



Setting aside for the present the peculiar adaptness and fitness of the 

 observer for his business, we are necessarily interested in the requirements of 

 geodetic operations and especially in the duties of the instruments by which 

 these are satisfied. In all geodetic work, portability, accuracy and mainte- 

 nance of instrumental adjustment are essential to rapidity of progress,to economy 

 of expenditure in money and in personnel, and to precision in the results. 

 Experience and theory teach us that in any given instrument, such as a theodo- 

 lite for geodetic purposes, we need simplicity of design; fewness of pieces; 

 harmony in the proportion of parts; accuracy of workmanship; superior gradu- 

 ation with adequate microscope micrometers; micrometer screws free from 

 mechanical defects; commensurate optical conditions of penetration and power; 

 sensitive and trustworthy levels; and the highest precision in all the bearings of 

 the moving parts. Moreover, the general disposition of the parts should be such 

 as to oflfer the greatest facilities to the observer, in order that he may make the 

 necessary observations without fatigue or nervous strain. 



Guided by these general considerations, I examined the fine collection of 

 geodetic instruments exhibited by the Minister of War, many of the exhibits 

 of private exposants, and some of the workshops of the manufacturers in Paris. 

 After this I visited the principal manufactories of Geneva, Neuchatel, Munich, 

 Vienna, Dresden, Berlin, Hamburg, Cassel, London and York. At the exposi- 

 tion I did not have the fullest facilities afforded me, and not only was I unable 

 to get into one of the principal cases, but I was positively forbidden to con- 

 tinue my drawings; whilst one well known maker would not only not permit 

 me to make any tests of the graduation of his theodolite, but would not allow 

 me see his graduating engine. Outside of Paris I was permitted to see every 

 graduating engine of the noted manufacturers, and afforded facilities for the ex- 

 aminations of their productions. But on account of the commercial depression 

 which was overshadowing all business in Europe, as well as the United States, 

 the number of the larger instruments on hand was very few. In some work- 

 shops I found that not over 20 per cent, of the usual number of workmen were 

 employed. 



Besides the mechanical construction of the instruments, I was particularly 

 anxious to study the capacities of the different graduating engines, in order 

 to judge, in a measure, of the probable value of the results. The graduating 

 engine is simply a mechanical tool with which we should expect to divide a circle 

 of say 20 inches in diameter in 360 parts, with no greater an error than the 

 1-50,000 part of an inch or 4-10 of a second of arc in any one degree. The 

 probable error of an experienced observer in reading the five minute gradu- 

 ations of such an instrument is about 1-10 of a second of arc, or the 1-200,000 

 of an inch. It is usually assumed that the graduation errors are not over one 



