794 



SEC. .15. GEOGRAPHY. 



The Southampton Institute has made several metrological studies. The 

 apparatus designed by Ibaner, which was connected with the bar constructed 

 by Borda, produced the most satisfactory results. 



The three other parts of this work refer to triangulations of the three groups 

 of the above-mentioned islands. The plates represent 



(a.) The bar of the Ibaner apparatus in two projections, mounted for 



observation. 



(6.) Details relating to the supports of the bar and its construction, 

 (c.) Microscopes ; glasses and other details of this apparatus. 

 (d.) Form, dimensions, and construction of the station marks established 



at the trigonometrical points of the 1st, 2nd, and 3rd order, 

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



1 st class triangles of the Balearic Islands. 

 (/.) Theodolite of 2nd class. 



(#.) Geodetic local networks interlacing the groups of the Balearic 

 Islands. Printed in three colours. The first class network is in 

 black, the 2nd in red, the 3rd in blue. 



(13.) Central base for Geodetic 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 chosen for the ge.odetic triangulation of Spain starts 

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

 surement gave a result of 14,664 m , + 0-0025, with a difference of level 

 between the extremes (Bolos y Carbonera) of 2 -482 + 0-01 O nl . 



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

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



The measurements adopted to fix the extremities of the base, and establish 

 a trigonometrical network by which it might be determined whether it was 

 necessary or not to measure bases of great extent, are all given in detail in 

 this work. The observations and calculations for the measurement and 

 levelling of the base, the triangulating studies and compensation of the net- 

 work, 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 ye o^ooo 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 measurement of the sections of the base 

 and their length deduced from the calculations of the trigonometrical net- 

 work, which gave the following results : 



