M. Savi on the Insalubrity of the Air of the Maremma. 233 



mensuras quae ceitae ac rarae apud omnes nationes haberentur." 

 He then gives the preceding table. Clavius would be, I 

 should think, a better authority than Riccioli on a habit of 

 the sixteenth century. 



It is not then a thing to be taken without further showing 

 that Fernel, a mathematician, writing for mathematicians, 

 used a French foot when he says he used a geometrical foot. 

 Even without the assertion relative to his own pace, as com- 

 pared with the geometrical pace of five foot-lengths, it seems 

 to me that there is ample ground on which to contest such 

 an assumption. If the writers of the sixteenth century had 

 had anything to do with the usual measures, they would some- 

 times have mentioned their diversity; instead of which there is 

 a uniform determination to avoid speaking of local measures, 

 and a continual reference to a system which is adopted in the 

 same words, with the same descriptions, and by writers of all 

 countries, Italian, German, French, or Belgian. That this sy- 

 stem was in practice a "curious fiction," is perfectly true, since, 

 though the difference between the results of one careful ap- 

 peal to the natural standard and another might be rather 

 small, there was no certainty of any agreement of even what 

 would then be called the closest kind. But, let their mode 

 of measurement be ever so defective, it voas their mode of 

 measurement, and Fernel must be held to have had recourse 

 to it until some reason is given for supposing that he chose to 

 be an exception. 



I remain, Gentlemen, yours faithfully. 

 University College, Feb. 12, 1842. A. De Morgan. 



XXXV. Considerations on the Insalubrity of the Air of the 

 Maremma. By M. Paul Savi, Professor in the University 

 of Pisa. 



[This me~.oir was read to the Geological Section of the Scientific Meeting 

 held at Pisa in October 1839, and [jublished in the Nuovo Giomale dei 

 Lilterati, Nos. 106 and 107. We have taken it from the yinnales de Chimie 

 et dc Physique for November last, in which it follows a translation of Pro- 

 fessor Daniell's paper ' On the Spontaneous Evolution of Sulphuretted Hy- 

 drogen,' &c. (Phil. Mag., Third Series, July 1841.) The French editor's 

 observations we also give. — Edit. Phil. Mag.'] 



npiIE important memoir of M. Daniell having directed the 

 -* attention of philosophers to the production of sulphuretted 

 hydrogen by the imitual action of sulphates and organized 

 bodies, we have deemed it proper to reprint M. JSavi's memoir, 

 which is but little known, but in which the same reaction is 

 indicated as one of the most powerful causes of malaria. 

 It is generally known that several parts of Tuscany and 



