338 Progress of Foreign Science. 



has become retrograde ; the mean annual amount of which is 

 = — 1' 57". The total retrocession between 1818 aud 1820, by 

 a comparison of the morning observations, is 3' 22" 



noon 4' 22' 



evening 4' 0" 



The Board of Longitude of Paris has established lately, at 

 the Observatory, a magnetic needle, exclusively consecrated 

 to indicate the diurnal variations of declinations. Some de- 

 rangement, from an unknown cause, having happened to it iu 

 1819, it was re-mounted last February, since which time its 

 march has been regular. The observations made with it indicate 

 already a retrograde movement of the needle towards the east. 

 The jnea?i declination of the month of February, 1821, is smaller 

 by 2' 15' than that of the month of February, 1820. — Ann. de 

 Chim. et de Phys. xvi. p. 54. 



We reserve several electro-magnetic notices for next quarter. 

 — "We intended to have given M. Moll's account of Colonel 

 OfFerhaus's apparatus, published in the Journal de Physique for 

 April last, in the form of a letter to the editor ; but, as we find 

 that the same letter is re-printed, with the date of June 22d, 

 in the Edin. Phil. Journal of October last, we are saved the 

 trouble of transcription. 



IV. Under the science of Mechanics, the most prominent 

 paper is that of M. P. S. Girard, on the uniform discharge of 

 atmospherical air and carburetted hydrogen gas, through 

 conducting pipes. We have no room for an analysis of it at 

 present. 



V. Natural History. — Baron Humboldt, in a memoir read 

 to the Institute 19th February last, 1821, entitled, "New Ob- 

 servations on the Laws which we observe in the Distribution of 

 Vegetable Forms," states, that we already know nearly 56,000 

 species of cryptogamous and phanerogamous plants, 44,000 

 insects, 2,500 fishes, 700 reptiles, 4,000 birds, and 500 species 

 of mammiferae. In Europe alone, according to the researches 

 of M. Humboldt and M. Valenciennes, there exist nearly 80 

 mammiferae, 400 birds, and 30 reptiles. There are, of conse- 

 quence, under this temperate boreal zone, 5 times as many 

 species of birds as of mammiferae ; as, in like manner, there are 

 in Europe 5 times as many compositae as amentaceous and co- 

 niferous plants ; 5 times as many leguminous as there are of 

 orchideous and euphorbiaceous. The fine collections recently 

 brought home from the Cape of Good Hope by M. Delalande 

 prove, (if we compare them with the works of M. M. Temmink 

 and Levaillant,) that in that part of the temperate austral zone, 

 the mammiferae are also to the birds in the proportion of I 

 to 4.3. Such an accordance between two opposite zones is 



