V. MAPS, ETC. 793 



microscopes in the line of the base, and another glass settles the beginning and 

 end of the day's work. 



This delicate apparatus cannot be sent out of the country ; it is preserved at 

 the Geographical Institute of Madrid. 



After this study was made, the expansion of the bars was investigated and 

 compared with that of Borda, at the Paris Observatory, which has served as 

 the standard of all the geodetic bases measured in France since 1798. 



The result of the studies is given in this work, and the manner of using this 

 apparatus and carrying out the calculations. 

 These plates represent 



(a.) Two of the projections of the bar and level mounted upon its supports 

 and tripods, and the microscopes placed to observe the lines of 

 division at the extremities. 



(6.) Details of the construction of the supports of the bar, the slow and 



quick movements which it is capable of making, the construction of 



the latteen and platinum bars, the details of the same divided into 



decimilimeters, and a drawing of the level of the bar. 



(c.) Details of the micrometer microscopes, circles, reference glass, 



lenses, and tracers, 

 (rf.) The comparator. Experiments to verify the studies of expansion in 



oil bath. 



(e.) Same in detail as the former. 

 (/.) Apparatus used by the observers in the construction and comparison 



of thermometers. 



(</.) Borda's bar with which the Spanish one was compared. 

 (12.) Geodetical description of the Balearic Islands, by Don 

 Carlos Ibaner. Madrid, 1871. 



The author was commissioned in 1864 to study the first of the geodetic 

 Catastralian districts, which are comprehended in the provinces of Castellon, 

 Valencia, Alicante, and Balearic Islands ; he verified it in the campaigns of 

 18G5, 1866, 1867, and 1868, and made the necessary studies to describe and 

 interlace the three groups formed by the islands of Tviza and Formentera 

 with surrounding islets, with those of Mallorca, Cabrera, and Dragonera, and 

 with the island of Minorca and adjacent islets. Each of these groups with 

 i.)s corresponding triangulations is divided by first, second, and third class 

 nets. 



Each local triangulation was founded upon a base measured by the 

 Ibaner apparatus, constructed by Messrs. Brunner. 



In the first part of this work will be found a description of the instruments 

 and accessories employed in this study, beginning with the new apparatus for 

 measuring bases. This consists principally of a plated iron bar, with four 

 thermometers of mercury and a plane table, placed upon tripods and supports, 

 microscopes, and lineation glasses, and reference to the beginning and end of 

 the daily work. This apparatus offers the greatest advantage over other 

 analogous instruments, for the rapidity and ease with which the measures are 

 taken, without losing the degree of exactitude required for a geodetic base. 

 It is to be employed to measure the three bases still wanting in the Spanish 

 geodetic net projected in the provinces of Cadiz and Lugo. 



The probable errors resulting from the measurement x>f the Balearic 

 Islands were 



Base of Ibiya +0-401 mm , or +0-00000240 of the length measured. 

 Base of Prat, Mallorca, + ]-681' nrn , or 0-000000794 of the measured 

 length. 



Base of Mahon (Minorca) +0'770 mm , or +0*000000326 of the length 

 measured. 



