2 PRACTICAL TREATISE ON 



the burning property of lenses made of glass. Ptolemy, the 

 celebrated astronomer of Alexandria, who flourished in the 

 latter part of the first century, was evidently cognizant of 

 the existence of magnifying glasses, and makes use of the 

 word refraction in his work on optics. The testimony of 

 these ancient writers, however, is only important as proving 

 the existence of the microscope in its 'most simple and rudi- 

 mentary form, viz., as an instrument composed of a single 

 magnifying glass or sphere, whose chief application appears 

 to have been that of concentrating the heating power of the 

 sun's rays. It is, however, certain that the simple micro- 

 scope, if we apply this term to every instrument used for 

 magnifying objects, first consisted of a sphere of glass or 

 globe, of the same material, filled with water ; these, no 

 doubt, were soon superseded by lenses of a bi-convex figure, 

 for, according to Dr. Francis Kedi, the latter were in use 

 early in the fourth century. To our countryman, Roger 

 Bacon, who was born at the commencement of the thirteenth 

 century, is attributed the invention of the telescope, the 

 camera obscura, the reading glass, and gunpowder, and, by 

 some, the discovery of the microscope, as he speaks, in his 

 Opus Majus, of principles applicable to it; Record, in 

 his work, entitled Chemin de la Science, published in 1551, 

 relates that Bacon, whilst at Oxford, made a glass which 

 exhibited such curious things, that its effect was generally 

 attributed to some diabolical power. Some centuries were 

 suffered to elapse before the microscope was again noticed, 

 and then we read of it in its improved or compound form, 

 as being supplied with two or more magnifying powers. 

 Several authors, especially Huyghens, assign the invention of 

 the compound microscope to Cornelius Drebbel, a Dutchman, 

 in the year 1621, whilst Fontana, a Neapolitan, claims the 

 discovery for himself in 1618. According to Borellus, it was 

 invented by Zacharias Jansen or Zansz, or his father Hans 

 Zansz, spectacle-makers at Middleburg, in Holland, about 

 the year 1590; they are said to have presented the first 

 microscope to Charles Albert, Archduke of Austria. " One 

 of their microscopes," says Sir D. Brewster, in his Treatise 



