562 



SCIENCE, 



[Vol. VI., No. 151. 



which made Captain Talcott's method easy of appli- 

 cation for field use at geodetic stations. Professor 

 Chauvenet says of the zenith telescope, — 



*' The method of finding the latitude by this instru- 

 ment, now known as Talcott's method, is one of the 

 most valuable improvements in practical astronomy 

 of recent years, surpassing all previous known 

 methods (not excepting that of Bessel by prime ver- 

 tical transits) both in simpUcity and accuracy." 



Soon it was found that observations by Talcott's 

 method, with the zenith telescope, were superior in 

 precision to the places of the stars observed as given 

 in the catalogue. Hence arose a demand for better 

 star-places ; and the observatories of the country 

 were called upon by the coast survey to furnish them, 

 the coast survey paying for the labor involved in 

 observation and reduction. The directors of the 

 observatories, finding their instruments and means 

 insufficient for the desired results, applied themselves 

 to procure better ; and thus again the coast survey, 

 by the stimulus it gave to astronomical means and 

 methods, added another to its list of aids given to the 

 advancement of American science. As a conse- 

 quence, in a large part due to this cause and to those 

 mentioned in what has been said respecting tele- 

 graphic determinations of longitude, we have at 

 present catalogues of star-places of a degree of pre- 

 cision of the highest order. 



In 1867, Assistant George Davidson invented and 

 added to our means an ingeniously contrived instru- 

 ment for observing both latitude by the Talcott 

 method, and local time as usual with a transit instru- 

 rnent, by one and the same instrument. This ' com- 

 bination instrument ' is now largely and successfully 

 used. 



Geodesy. 



All contributions by the coast survey to science in 

 this department must, of necessity, be practical in 

 their character, since the principles involved in the 

 application of all geodetic methods are as old as 

 Euclid. 



Improvement in accuracy of geodetic instruments 

 of every class, and especially in improving their pre- 

 cision while diminishing their size and weight, has 

 been marked and steady from 184:4 to the present 

 time. More precise observations are now obtained 

 with a theodolite having a graduated circle of twelve 

 inches diameter than could be had in 1844 with in- 

 struments having circles of twenty-four and thirty 

 inches diameter. When it is considered that these 

 instruments are transported to the highest summits 

 of North America, often upon the backs of mules, it 

 will be perceived what a gain to precise scientific 

 observation is obtained by the diminishing of weight. 



The substitution of the observation of directions 

 for that of angles is another gain to science. The 

 change of the problem to be ascertained by observa- 

 tion, from ' What is the most probable measure of a 

 certain angle ? ' to ' What is the most probable direc- 

 tion of a certain line ? ' has added greatly to ease of 

 observation, and precision in results. 



Methods of determining azimuth, or the angle 

 made by any geodetic line with the meridian of the 

 place of observation, have been simplified and mul- 

 tiplied, and increase of precision obtained, with less 

 labor and in less time. 



Wherever it had become necessary to use artificial 

 elevations for geodetic observations, it had been usual 

 in Europe, India, and America, to use repeating 



theodolites which only required temporary stability, 

 not usually exceeding a couple of minutes at a time. 

 For important primary stations, brick towers were 

 erected ; or, if wooden towers were used, they were 

 carefully enclosed to protect them from the sun's 

 action. But in 1868, Professor Peirce, then superin- 

 tendent of the coast survey, authorized the use of 

 open wooden insulated tripods for supporting the 

 larger direction instruments of the coast survey. 



The legs of the tripods were exposed to the ful) 

 action of the sun's rays, while shaded by light cotton 

 screens from the force of the wind. The motion of 

 the wooden tripod caused by the action of the sun's 

 rays was eliminated from the result by the method of 

 observation adopted. Since that period the largest 

 and most delicate theodolites have been successfully 

 used upon cheap wooden structures in many parts of 

 the country, and money and time saved with no 

 falling-off in precision. 



Within the past ten years the old methods in vogue 

 a century ago, of observing upon intensified lights 

 at night, have been renewed, using both magnesium 

 and coal-oil reflector-lamps, and much time has been 

 saved by adding to the number of hours when 

 observation was possible. The precision of the work 

 has also gained by night observation. 



Topographical methods have also been improved. 

 The use of the plane-table has been extended, and this 

 unrivalled method of executing precise maps, by mak- 

 ing and correcting them upon the ground itself, is now 

 regularly taught in some of our scientific schools, as 

 are other coast-survey methods of observation, reduc- 

 tion, and computation. In every institution of learn- 

 ing in this country, at Cambiidge, New Haven, New 

 York, Ithaca, the coast survey has left its impress, 

 and everywhere for good. 



The coast survey is as well able to continue its 

 course now as it ever has been. Its ofiicers are as 

 able and zealous as they were twenty years ago. Its 

 form of organization has proved itself well adapted 

 to its needs, and, with some essential changes to 

 cause it to conform more closely to the changed ex- 

 ternal conditions, it may do the country thorough 

 and vigorous service. It is to be devoutly hoped that 

 the opportunity may be given it to prove what it is 

 made of, and that its force may be more concen- 

 trated, instead of being broken up and scattered. 



C. O. BOUTELLE, 



Asst. U. S. coast and geod. surv. 



An old work on political economy. 



The last numbers of Science brought to my memory 

 the time of 1842, when I studied in Paris, and had, 

 by the request of my father, professor of political 

 economy, to procure for him a large number of 

 books and tracts on political economy. Some of them 

 were very rare, even in the libraries, and I had to 

 content myself with making out a very full and de- 

 tailed account of their contents. Among them was, 

 * Traite del'oeconomie politique, dedie au roi,' etc., by 

 Antoine de Montchretien, seiur de Vateville ^ Eouen, 

 1615 pet. 4°. The book was only to be found in the 

 Bibliotheque Mazarine and St. Genieve, not in the 

 Royal library. It was considered very rare The 

 book is interesting, as the phrase * political economy ' 

 is first used in it, and its author considered to be its 

 founder. The book is very interesting, praises TuUy 

 and his maxims, and is decidedly strong for protection. 

 There are also to be found in it a number of curious 



