V. MAPS, ETC. 



665 



(df.) Form, dimensions, and construction of the station marks given in the 

 vertices of the 1st, 2nd, and 3rd order. 



(e.) The theodolites employed for the azimuth and zenith observations of 

 1 st class nets of the Balearic Islands. 



(y.) Represents a theodolite of 2nd class, and the observation tints em- 

 ployed to measure the bases. 



(<?.) Geodesical local nets interlacing the groups of the Balearic Islands. 

 Printed in three colours. The first class net is in black, the 2nd in 

 red, the 3rd in blue. 



They prove that in a scale of $ 00 1 000 m 5 kilometers topographic will 

 always meet with a geodesical vertex perfectly and accurately determined. 



(13.) Central base for Geodesical Triangulation in Spain, by 

 Don Carlos Ibaner. Lieut.-Col., &c., Don Frutos Saavidra, Don 

 Fernando Monet, and Don Cesario Quiroga ; Madrid, 1865. 



The parting line chpsen for the geodesian triangulation of Spain starts 

 from the central base of Madridejos (province of Toledo). The direct mea- 

 sure gave a result of 14'664 m , 5-000 + 0'0025 m , with a difference of level 

 between the extremes (Bolos y Carbonera) of 2'482 + O t 010 m . 



These studies were carried out by the gentlemen mentioned on the title- 

 page of the book, by means of the apparatus of Ibaner. 



The measures adopted to fix the extremes of the base, to trace the lineation 

 of its five sections, and establish a trigonometrical net by which it might be 

 determined whether it was necessary or not to measure bases of great ex- 

 tension, are all given in detail in this work. The observations and calcu- 

 lations for the measurement and levelling of the extremes of the base, the 

 triangulating studies and compensation of the net, and the final results of this 

 operation are also mentioned. 



The results of these operations, and their precision, may be judged by the 

 probable error of measurement, which has already been mentioned, as 

 + 0-0025 m , or j. 80 ^ 000 of the length of the base. 



In order to decide the question of the extent of base line requisite, a com- 

 parison was made between the direct measure of the sections of the base and 

 their length deduced from the calculations of the trigonometrical net, which 

 gave the following results : 



These remarkable results proving the direct measurement, at the same time 

 give authority for reducing the length of the geodesical base to two or three 

 kilometres, that is, whenever they are connected with the sides of the net by 

 means of a system of lines suitable for compensation. This is the first 

 experimental result of the kind given in geodesy. 



