S64 Mr. Swainson's St/nopsis of ike Birds of Mexico. 



relatively to the under surface of the level *, but have also the 

 effect of disturbing for some time the adjusting screws, and pro- 

 bably other parts of the mounting. On measuring by an ad- 

 justed level a number of planes or lines differing in inclina- 

 tion, the half-difference of the space passed over by the bubble 

 should always be zero, or the instrument cainiot be considered 

 as })erfect. 

 Leeds, March 5, 1827. 



Erratum.— Pase 2G0 ; for 200,000, read 206263 ; (the number by which 

 the lengtli of a cHvision on the scale of a level answering to 1" must be 

 luultipHeil to obtain the length of the radius of its CLirvature). 



LXXII. A Si/7iopsis of the Birds discovered in Mexico by 

 W. Bullock, F.L.S. and H.S., and Mr. William Bullock, 

 JwL Bj/ William Swainson, Esq. F.R.S. F.L.S. c^cf 



THE intercourse which recent political events have opened 

 between Mexico and Great Britain, promises to be no 

 less interesting to zoological science, than important to the 

 commercial prosperity' of both nations. Mr. Bullock was 

 among the first of our countrj'men, whose ardent curiosity led 

 him to visit those distant shores ; and the scientific treasures 

 with which he returned, bear ample testimony to that zeal and 

 indefatigable industry which has ever marked his pursuits. 

 The exhibition of these objects, together with the valuable 

 models and relics of Mexican antiquity, which this enterpri- 

 sing traveller procured during the short space of his sojourn, 

 attracted the public attention for two years. That such a col- 

 lection, invaluable to the historian as throwing a new light 

 upon the ancient state of one of the most extraordinary nations 

 of antiquity, should have been suffered, in these days, to have 

 been dispersed by the hammer of the auctioneer, will excite 

 the deep regret of every friend to knowledge. They may now, 

 indeed, serve as objects of mere curiosity, but those advan- 

 tages which the historian and the antiquary might have de- 

 rived from their study and investigation, as a whole, are for 

 ever lost. 



The zoological subjects, possessed by no museum in Europe, 

 shared the same fate, but not before Mr. Bullock had placed 



* When the temperature increases, the verte.\ removes to a point of the 

 tube nearer the tliickcr cud. In some levels now in my possession the va- 

 riation is 1" for every ;l degrees of Fahrenheit's thermometer. 



f Comnuinicated by the Author. 



the 



