40 Mr. A. H. Haworth on some new Cacti and Mammillaria?. 



height of a column of mercury that will balance the pressure 

 of the atmosphere; and put Z> = 7*3. Thus, if these values be 

 substituted in the equation No. 2, and different values taken 

 for y, we shall thereby obtain the corresponding values of .r, 

 or the height of the column of mercury in the tube C, indi- 

 cating the several pressures. Thus, put y = 30 atmospheres; 

 then 



<r= 477*25- V 227767-54-45312 + 560-64-67968 



x= 23 - 74 inches. 



That is, the altitude of the mercury in the tube will be 23*74 

 inches, when the pressure is equal to 30 atmospheres pressing 

 upon the surface of the mercury in the lower chamber B. 

 And in this manner have been computed the different values 

 of a-, corresponding to different pressures, as shown in the 

 following table: 



Table for graduating tlie Scale. 



Values of x Values of x 



Pressure. or height of Pressure. or height of 



the mercury. the mercury. 



21 atmospheres 2-49 inches. 31 atmospheres 25*42 inches. 



VIII. Descriptions of some new Cacti and Mammillarise, re- 

 cently brought from Mexico by Mr. Bullock of the Egyp- 

 tian Hall, Piccadilly ; and notv preserved, "with many other 

 very rare Plants, in the Nursery of Mr. Tate, in Sloanc- 

 street. By A. H. Haworth, Esq. F.L.S. Sj-c. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 



A LLO W me to transmit to you herewith technical descrip- 



"^*- tions of some new and very remarkable plants of the 



family of Cacti Juss., which I hope you will admit into an 



early Number of your valuable Miscellany. And I remain 



Your most obedient servant, 



Queen's Elm, Chelsea, Nov. 1823. A. H. Ha WORTH. 



Cacti 



