NATUEAL PHILOSOPHY. 171 



Nor have these discoveries been the mere amusement of dilettanti 

 philosophers. The observation of these minute forms of life has led 

 to a more correct and satisfactory knowledge of the nature and forms 

 of higher and more visible creations, and there are no botanists or 

 zoologists in the present century who, like Linnaeus in the last, would 

 reject the microscope as interfering with the natural history and 

 arrangement of those creations which are visible to the naked eye. 



lUit the bringing to light of new forms of animal and vegetable life 

 is perhaps the least half of what the microscope has done for science. 

 In permitting observations to be made on the minute structure of the 

 parts of plants and animals, it has given a deeper insight into the 

 laws by which they exist and the nature of the special functions they 

 are destined to perform. Let any one compare the physiology of 

 2o years since, as given in the manuals of that day, with what it is now. 

 It will be seen at once how vast has been the progress made. Al- 

 though Malpighi first saw blood-cells, the researches of modern 

 microscopists have given correctness and precision to our present 

 knowledge of that great source of animal life, the blood. It is to 

 the start given by Schleiden, through his microscopical researches, in 

 1838, in the nature of vegetable cells, so ably followed by Schwann, 

 in a series of kindred researches in animal cells, that the great science 

 of histology owes its existence. It is in the changed nature of the 

 cells of the living tissues that the pathologist looks for the exposition 

 of the true nature of disease ; and although the slovenly practitioner 

 of medicine may not be aware of the cause, the vicw r s of disease, 

 which are modifying the practice of medicine every day, are mainly 

 owing to the formation of more correct theories of disease under the 

 influence of the microscope. 



The history of the manufacture of this instrument is curious. Not 

 above 25 years ago, when the London Microscopical Society w r as first 

 established, it was customary for the President of that Society, in his 

 Annual Address, to state the number of microscopes manufactured 

 by the great houses in London in the course of the year. This prac- 

 tice has long been discontinued, as many houses turn out microscopes 

 by the thousand in the course of a single year. By this demand, too, 

 the instrument has been vastly reduced in price, and the great opti- 

 cians svho still manufacture microscopes that cost 100 when com- 

 plete, 'sell instruments of great excellence at the low price of five 

 guineas. London Afhenceum. 



MICROSCOPIC STRUCTURE OF IRON AND STEEL. 



At the British Association, 1864, Mr. H. C. Sorby exhibited "Micro- 

 scopical Photographs of various kinds of Iron and Steel." He first 

 described the manner in which the sections of iron and steel are pre- 

 pared for microscopical examination. The final process consists in 

 reeling with very dilute acid on level and perfectly polished surfaces, 

 showing no scratches, even when examined with the microscope. 

 The acid, acting on the different constituents, or on different crystals, 

 in a variable manner, causes the structure to be exhibited in very 

 great perfection, by various colors or tints. He then explained the 

 precautions required in taking enlarged photographs direct from the 

 prepared surfaces of iron or steel, and exhibited a series photographed 



