PER 



FER 



also a good taste in astronomy, and natu- 

 ral and experimental philosophy, and was 

 possessed of a happy manner of explain- 

 ing himself in an easy, clear, and familiar 

 way. His general mathematical know- 

 ledge, however, was little or nothing. Of 

 algebra he understood but scarcely more 

 than the notation ; and he has often told 

 Dr Hutton, he could never demonstrate 

 one proposition in Euclid's Elements, 

 his constant method being to satisfy him- 

 self as to the truth of any problem with a 

 measurement by scale and compasses. 

 He was a man of a very clear judgment 

 in any thing he professed, and of unwea- 

 ried application to study ; benevolent, 

 meek, and innocent in his manners as a 

 child ; humble, courteous, and communi- 

 cative : instead of pedantry, philosophy 

 seemed to produce in him only diffidence 

 and urbanity. 



The list of Mr. Ferguson's public works 

 is as follows: 1. Astronomical Tables and 

 Precepts for calculating the true times of 

 new and full Moon, &c. 1763. 2. Ta- 

 bles and Tracts, relative to several Arts 

 and Sciences, 1767. 3. An easy Intro- 

 duction to Astronomy for young Ladies 

 and Gentlemen, 2d edit. 1769. 4. Astro- 

 nomy explained upon Sir Isaac Newton's 

 principles, 5th edit. 1772. 5. Lectures on 

 select subjects in Mechanics, Hydrosta- 

 tics, Pneumatics, and Optics, 4th edit. 

 17/2. 6. Select mechanical Exercises ; 

 with a short account of the Life of the 

 Author, by himself, 1773. 7. The Art of 

 Drawing in Perspective made easy, 1775. 



8. An Introduction to Electricity, 1775. 



9. Two Letters to the Rev. Mr. John 

 Kennedy, 1775. 10. A third Letter to 

 the Rev. Mr. John Kennedy, 1775. 



FERMENTATION. The word fermen- 

 tation, in general, is used to denote that 

 change in the principles of organic bo- 

 dies, which begins to take place sponta- 

 neously as soon as their vital functions 

 have ceased, and by them are at length 

 reduced to their first principles. This 

 has been distinguished into three stages, 

 the vinous or spirituous, the acid or ace- 

 tous, and the putrid fermentation. It is 

 ascertained almost beyond doubt, that the 

 vinous fermentation takes place only in 

 such bodies as contain saccharine juices. 

 In this the most remarkable product is a 

 volatile, colourless, slight inflammable 

 fluid, which mixes with water in all pro- 

 portions, and is called alcohol, which see. 

 The acetous fermentation is distinguished 

 by the product known by the name of 

 vinegar, which is the least destructible 

 of the vegetable acids. It does not ap- 



pear, however, that fermentation is abso* 

 lutely necessary for the production of 

 this acid, as there are many other chemi- 

 cal processes by which it may be obtain- 

 ed or produced. In the putrid fermenta- 

 tion, bodies appear to be red-iced into 

 their most simple parts. Ammonia is the 

 product which has been remarked as 

 the chief of this process, and is no 

 doubt produced by the combination of 

 the hydrogen and nitrogen gases, which 

 are disengaged together. See AMMO- 



NIA. 



The acetous, like the vinous fermen- 

 tation, is confined to vegetable sub- 

 stances ; but the putrefactive process is 

 most eminently perceived in animal bo- 

 dies. These either putrefy immediately ; 

 or, if the putrefaction be preceded by 

 either of the other stages, their duration 

 is too short to be perceived. It is con- 

 sidered as an established fact, that the 

 three stages of fermentation always fol- 

 low in the same order in such bodies 

 as are susceptible of them all ; the 

 vinous coming first, which is followed 

 by the acetous and the putrefactive pro- 

 cesses. 



The spontaneous decomposition of bo- 

 dies is retarded by extreme cold, by sud- 

 den drying of the parts or by preserva- 

 tion in closed vessels. The two first cir- 

 cumstances necessarily retard the chemi- 

 cal effects, by depriving the parts of that 

 fluidity which is almost indispensably 

 necessary in chemical processes. It will 

 easily be understood that the third con- 

 dition will retard the spontaneous de- 

 composition of bodies, when it is consi- 

 dered that the atmosphere itself is the 

 solvent, or at least the receptacle of many 

 of the component parts of bodies with 

 which it is disposed to unite. In well 

 closed vessels the parts of organized bo- 

 dies, which are disposed to fly off in the 

 elastic state, are prevented from escaping; 

 and such parts as might form new combi- 

 nations, by absorbing either the contents 

 or the component parts of the atmos- 

 phere, are prevented, for want of a free 

 communication. The three conditions 

 for the accomplishment of fermentation 

 are, therefore, fluidity or moisture, mo- 

 derate heat, or a due temperature, and 

 the access of air ; the fermentation will 

 likewise be modified according to the 

 various component parts of bodies. 



In describing the vinous decomposition 

 of vegetables, it will be of advantage to 

 attend to that of mere sugar and water; 

 the phenomena in these being more dis- 

 tinct, because less modified by foreign 



