200 



KNOWLEDGE. 



[SEPTEMnEU 1, 1896. 



most diflicuU testa known to microscopists. Water immer- 

 sion lenses were constructed by Englishmen about 18110, 

 who made both new lenses and also new front combinations 

 to screw on to old glasses. About twenty years ago a 

 farther great advance was made by l\Ir. J. \V. Stephenson, 

 of the r>ank of I'ngland, who induced the firm of Zeiss, of 

 Jena, to construct lenses in which a drop of cedarwood oil 

 was substituted for water. These were termed homo- 

 geneous immersion lenses, because the oil being of the 

 same refractive index as the glass of which the objective 

 was made, the light from the object passes into the 

 optical system without refraction. ]5ut for greater im- 

 provements still we are indebted to the optical knowledge 

 of Prof. Abbi', of Jena University, in combination with 

 the mechanical skill of the late Carl Zeiss. In every 

 achromatic object-glass it is impossible to unite more 

 than two rays of the dispersed light in the spectrum, viz., 

 red and green, the others being left out and forming what 

 is called the secondary spectrum. It occurred to the 

 Professor to construct an objective with the mineral fiuorite 

 — which has a very low refractive index — as a component, 

 and so to obtain a greater command over the removal of the 

 chromatic dispersion. He thus devised what are now 

 known as apochromatic objectives, which are slightly over- 

 corrected for colour, while the eyepieces used with them 

 are under-corrected, the result being that three rays of the 

 spectrum are united and an almost colourless image is 

 produced. The magnification by means of these eyepieces 

 may be carried to a large extent, eyepieces having a 

 magnification of twenty-five times being used with these 

 objectives without any apparent degradation as regards 

 colour, especially with the lower powers. This discovery has 

 been followed by every optician of note, both here and on 

 the Continent, and it may be truly said that no scientific 

 work of any importance with the microscope can be done 

 without an apochromatic objective. The microscope has 

 by this means been firmly established on a footing which 

 the telescope can never, we fear, hope to possess. It 

 " holds the head " in optics, as our French neighbours say. 

 It is much to be regretted, however, that we are so very 

 dependent upon foreign workmanship for the optical tools 

 with which important scientific work is done. Oar British 

 manufacturers are no longer leading but following, for 

 most of the firms are making microscopes upon what is 

 called the " Continental model," the instruments with 

 which nearly all real scientific work is done at the present 

 day. 



A QUARTER OF A CENTURY'S WORK ON 

 RESPIRATION. 



By C. r. TowNSEND, F.C.S. 



AMONG the achievements of this century, the 

 advance that has been made in our knowledge 

 of physiology will not be the least. The brain 

 and the various glands, however, have absorbed 

 the lion's share of attention, and, until the work 

 of Drs. Haldane and Lorraine Smith awoke renewed 

 interest in the subject, the study of the lungs had been 

 largely neglected. Of the few who have devoted them- 

 selves to this branch of research, Dr. W. Marcet, F.R.S., 

 has been the most constant, and has given a large part of 

 his life to the solution of the problems connected with 

 respiration. His investigations have not been confined to 

 the laboratory, but have been conducted frequently in the 

 open air at varying elevations, extending from sea-level 

 to the summit of the Breithorn. Most of the results are 



scattered through the TmnH/ictions and Procpciliruin of 

 till- lidi/iil Socirii/ : but recently Dr. Marcet, as Croonian 

 Ijecturcr to the Royal College of Physicians, had an 

 opportunity of summing up the whole of his work. 



The early experiments during three summers in Switzer- 

 land gave decidedly interesting results. The following 

 stations were chosen : — 



1. Yooire on the Lake of Geneva 1,280 feet. 



2. The Hospice of the Great St. Bernard 8,115 „ 



3. The Eiffel Hotel, Zermatt 8,128 „ 



1. The Hut in the St. Theodule Pass ... 10,899 „ 

 5. The Summit of the Breithorn ...13,685 „ 



The person under experiment breathed through a face- 

 piece made to cover both mouth and nose, and fitted with 

 ebonite valves, so that the air coming from the lungs 

 (expired air) should pass without loss to the receiver — a 

 large india-rubber bag, communicating with the face-piece 

 by a flexible tube. Breathing was commenced at a given 

 signal and continued until a definite volume of expired air 

 had entered the bag. The time required for the lungs to 

 expire this volume of air was determined accurately by 

 means of a stop-watch. The results showed an increase 

 of carbonic acid given off, equivalent to increased 

 combustion at high altitudes in the Alps. The actual 

 weight of air breathed in a given time was less, however, 

 at high altitudes than at the seaside. It follows that 

 breathing is easier in the Alps than in the plains. 



In order to ascertain whether the increase in the 

 carbonic acid given off from the lungs, and consequent 

 greater chemical action, was due to cold or to altitude. 

 Dr. Marcet, in 1878, determined to proceed to Tenerifl'e, 

 with the necessary apparatus for continuiug the research. 

 The baggage included a shed of wood and canvas made to 

 take to pieces, a chemical balance, a number of sealed 

 bottles full of standard baryta solution for the deter- 

 mination of carbonic acid, tubes filled with calcium 

 chloride for the determination of the moisture in the air 

 exhaled from the lungs, provisions, and everything necessary 

 for camping out on the Peak for three weeks. An Alpine 

 guide from Chamounix, who had assisted the investigator 

 in his previous expeditions, again accompanied Dr. Marcet. 

 The great advantages of Teneriffe for this work were, 

 first, its accessibility ; secondly, its dry climate and its 

 Peak, which rises sheer out of the sea to a height of over 

 twelve thousand feet ; but mainly the fact that stations 

 could be selected at various heights on the Peak, varying 

 but little in their respective temperatures. 



In his book on " Southern and Swiss Health Resorts " 

 Dr. Marcet gives a very interesting account of his expedi- 

 tion up the Peak. The first station was at the foot of 

 Mount Guajara (seven thousand and ninety feet), and the 

 camp was made on a patch of white baked clay in the old 

 crater, which is now mostly a chaotic field of lava. The 

 landscape is the most desolate and dreary that could be 

 imagined, nothing but lava and volcanic rocks with an 

 occasional patch of sand or clay baked by the sun, and a 

 few straggling bushes of Bhctcvna — a kind of broom. The 

 heat everywhere on the Peak seems to be very great whilst 

 the sun is shining. Mr. Piazzi Smith, who was engaged in 

 astronomical work on the Peak, found the temperature in 

 the sun on the summit of Mount Guajara to bs 212-4° Fah. 

 It must have been but slightly less than this at Dr. Marcet's 

 camp in July and August, although the cold was great at 

 night. The radiation was intense, water left out in the 

 open all night becoming a solid block of ice by the morning. 

 The dryness of the atmosphere on the Peak was quite as 

 remarkable as the heat. The skin became dry and scaly, 

 so that it was almost painful to touch anything. Fresh 

 meat brought up from Puerto Orotava kept good for any 



