430 Mr. Haworth's Arrangement of Saxifragese. 



other larger circles, which the mind's eye may imagine to be 

 composed of several, one within another ; or, when taking the 

 widest possible range, the whole may be conceived to be but 

 or reiteratedly compounded circle, vast and grand, enfolding 

 or representing in its ample orb the mighty works of God on 

 earth. I have the honour to remain, sir, yours, &c. 



Queen's Elm, Chelsea, June 5, 1825. A. H. Haworth. 



Postscript. — It may be worth adding, that the first time 1 

 ever observed the prevalence of a dichotomous distribution in 

 nature, was in the winter of the year 1813-14, when engaged 

 in arranging and grouping the genera for my Saxifragearum 

 Enumeratio ; which, although shown soon after to some friends, 

 was not published until 1821. The distribution of the genera 

 there given is virtually and in spirit a dichotomous one 

 (though I did not then venture to print it so) ; and this will ap- 

 pear by the conciseness and precision of the following table, 

 which really alters not either the natural or current location 

 of a single genus there published. — Vide Saxifrag. Enum. p. 4. 

 — The genera are in italics below. 



SAXIFRAGEARUM TABULA DICHOTOMA. 



pllKIVALVES. 



pRectocalycatae. 



i-Acaules. — Megasea, Dermasea, Chondrosea. 

 ■-Foliosae. — Miscopetalum, Lobaria, Tridactylites, Saxifraga, 

 Muscaria, Leptasea, Hircidus, Ciliaria, Antiphylla. 

 "-Reflexocalycatae. 



pSessilifoliae*. — Micranthei... 

 Lpetiolatae. 



r-Decurrentes. — Aulaxis, Spatularia. 

 •-Edecurrentes. 



CSarmentosae. — Ligidaria... 

 Esarmentosae. — Robertsonia . . . 



l-Bl VALVES. 



j-Decandrae. — Mitella, Tiarella, 

 Lg — 5-andrae. 



pUniloculares. — Ckri/sosplenium, Adoxa. 



LBiloculares. — Heuchera . . . 



LXIX. Description of an improved Cross for Land-Surveyors. 

 By Mr. Isaac Newton. 



To the Editor of the Philosophical Magazine and Journal. 



Sir, 



IT being generally allowed and experienced by land-surveyors 

 that the measuring of diagonals, perpendiculars, &c., by 

 means of the chain and the common cross, is attended with a 



* Misprinted " Sessiliflorae" in Saxifrag. Enum. p. 4, &c. but not in p. 45. 



good 





