4 Mr. T. D. Aldous on the 



much older than myself as Dr. Hooke, hut I would with very 



great respect submit that if one looks at an object "a million 

 times smaller than a visible point," it is necessary to magnify it 

 a million times in order to make it appear as large as a visible 

 point, or, in other words, to see it at all ; and as with our 

 modern instruments, using, say, Jg oil immersion objective and 

 a Zeis No. 5 ocular, we get an amplification of 2020 times only, I 

 think we must make some allowance for enthusiasm in Dr. 

 Hooke's concluding statement. 



There were various makers and modifications in the details of 

 the manufacture of these globules, and one of the most dexterous 

 was a Neapolitan named Di Torre, who, after giving a detailed 

 account of the mode of their manufacture, concludes by saying : 

 — " In damp weather, notwithstanding every precaution, it will 

 often happen that, out of forty globules, four or five only will be 

 fit for use." 



Now we come, in the history of single microscopes, to about 

 the year 1673, and meet a familiar name, Leuwenhoek, who 

 made so many discoveries. He seems to have used entirely 

 single microscopes ; each of them consisted of a very small 

 bi-convex lens set in a socket formed by two metal plates 

 riveted together, and, of course, pierced with a small hole at 

 the centre of the lens. He had many such instruments of 

 varying powers to suit the various objects he examined by 

 attaching them to a silver point or needle capable of being 

 moved in any direction. Some of these instruments are, I 

 believe, in the possession of the Eoyal Society ; they did not 

 magnify so much as the glass globules, but, as Leuwenhoek 

 truly remarks, in a letter to the Society, " that from upwards of 

 forty years' experience" he found that the most considerable 

 discoveries were to be made with such glasses as, magnifying 

 but moderately, exhibited the object with the most perfect 

 brightness and distinctness. 



Here I must mention the very ingenious device of a Mr. 

 Stephen Gray, of Charterhouse, who in 1696, looking through a 

 glass globule which had some defects, noticed that these defects 

 were much magnified ; thereupon he conceived the idea that if 

 he could get a drop of water containing animalculae, he would 

 see them much magnified. This he did by getting a drop of 

 water known to contain animalculae on the end of a piece of 

 brass wire, and he says : — "On applying this to the eye he found 

 to his astonishment that those scarcely discernible with his 

 glass globules appeared as large as ordinary-sized peas." Another 

 enthusiast. Still, the idea was ingenious ; and he went further, 

 for he contrived another water microscope, consisting of two 

 drops of water separated in part by a thin brass plate, but 

 touching near the centre, which were thus rendered equivalent 



