Aug. 31, 1883.] 



♦ KNOWLEDGE • 



181 



been washed out in the former processes. If bhe films 

 have lost all their air-bubbles they may not iloat, but 

 stirring the water will make them do it, and a few small 

 pieces can be fished out with a thin spoon or a knife-blade, 

 and dropped on to a glass slide. They must then be spread 

 out very carefully with fine needles stuck in wooden 

 handles, or a tine sable pencil such as miniature painters 

 use. The object is to get some films spread out 

 quite flat. They will most likely be found folded up, or 

 one over another. The least force tears them, but under 

 a hand-magnifier or a dissecting microscope success is 

 easily obtained. Having arranged a few films nicely in a 

 water-drop, the slide should be allowed to dry slowly where 

 no dust can get at it. When it is quite dry, put a drop of 

 Canada balsam, thinned with benzine, on to a glass cover, 

 and press it gently on to the films. The cover may be 

 held with a spring clip, such as opticians sell for the pur- 

 pose, and the balsam must be allowed to harden before 

 the slide is fit for use. A hint may be given about the 

 Canada balsam. It is much too thick for most purposes in 

 the state in which it is usually sold. Pure benzine, or 

 benzole, as it is also called, dissolves it readily, so much so 

 that it is very useful in cleaning the superfluous balsam 

 oft" slides. When used for thinning, it must be added cau- 

 tiously, and the balsam bottle put in a warm place. When 

 it is about as thick as golden syrup treacle — not quite thin 

 enough for the films — further additions of benzine act 

 rather suddenly, and the thinning may be carried too far. 

 If so, the e.xtra supply can be evaporated ; but it is well to 

 hit the right quantity. 



Amongst the objects which yield beautiful results with 

 the acid and chlorate of potash treatment are the needle- 

 shaped leaves of the pine-trees. Pinus Auntriiica, common 

 in shrubberies, is a good one for the purpose. Quite clean 

 leaves should be selected, of fresh growth. They should be 

 cut into short lengths, so as not to require much acid to 

 cover them, and treated exactly as the Deutzia leaves, but 

 they want a little more cooking. When finished they are 

 quite white, and in the state of hollow tubes, all their insides 

 being eaten out. To prepare for the microscope, a piece of 

 the tube must be slit opeft and flattened out on a slide 

 with fine needles in a drop of water. If it curls up it 

 must be flattened again and kept so by a covering-glass. 

 When quite dry, mount in balsam, and view with a half- 

 inch objective polarised light and a selenite film. A hand- 

 magnifier is sufiicient to show that fir needles are orna- 

 mented with rows of white glistening spots. In these the 

 stomata of the plant are situated. Their action upon 

 polarised light is very beautiful, and the changes obtainable 

 by rotating tlie prisms very striking. Very elegant 

 patterns that would be popular for ladies' dresses, window- 

 curtains, itc, readily appear. So far as the writer knows, 

 these pine needles have been generally neglected by 

 microiicopists. 



TRICYCLES IN 1883. 



SMALL WHEELS v. LAKGE WHEELS. 

 By John Browning, 



Chainnan of the London Tricycle Chtb. 



CONSIDERATIONS of space prevented me from ex- 

 hausting this subject in my last article, though I had 

 left several points of great importance untouched on. 



The weight of machines witli large wheels is nev(>r felt 

 so injuriously as when pushing up hill. It has lieen roughly 

 calculated that out of each ten miles of road in England 

 one mile, at least, will be a hill too steep to be ridcal)le. 



Let any person take a ride of, say, even fifty miles in a 

 day on a tricycle with small wheels, weighing 60 lb., over a 

 moderately hilly road, and then repeat the ride over the 

 same course on a machine with, say, 52-in. wheels, weighing 

 961b. to 98 lb., which is a common weight for such a 

 machine. After pushing this machine up the hills, I will 

 warrant he will have had enough of large wheels. 



Last year I rode a " Premier Sociable," with 48-in. 

 wheels. As I wished to drive the machine throughout the 

 day, if I pleased, without my wife once putting her feet on 

 the pedals, I had it geared down to 36 in. The weight of 

 this machine was 172 lb. My pace, when riding with my 

 wife, was about four miles an hour, and our journeys 

 averaged twenty miles a day. 



This year I have been riding an " ApoUo Sociable " I had 

 specially made for me, with 44-inch wheels geared down 

 to 36 inches, as in the former case, but the weight of this 

 machine is only 1331b. Our pace on this is improved to 

 five miles an hour, and we average about 30 miles a day 

 with ease, and have ridden 7i miles within forty minutes, 

 and 23 miles in four hours. These we did easily, though 

 I pushed the machine vip more than three miles of bills 

 alone. With the additional experience I have now gained 

 I consider I should have done better by having the 

 " Apollo " made with 36-inch wheels geared level 



I thoroughly disagree with all gearing-down. When a 

 low gearing is required, let the wheels be made small 

 instead, and the rider will have a lighter, stronger, and 

 more compact machine. 



Weight is not everything, I admit ; but tricyclists must 

 make it the first consideration. It is the principal cause 

 of the exhaustion often complained of by riders. When 

 I rode a single machine which weighed 109 lb., I could 

 only ride fifteen miles without requiring a meal. Now I 

 have a machine which weighs just over 50 lb., I commonly 

 ride twenty-five miles between meals, and I have ridden 

 twenty-nine miles without refreshment. 



Regarded as performances these examples are, of course, 

 very poor, but being born almost without muscles, I am 

 compelled to ride with my brains, and my illustrations are 

 none the less useful on that account. 



Another point greatly in favour of small wheels is that 

 they oft'er scarcely any resistance to wind compared to 

 large wheels. I have frequently seen men almost pulled 

 up by wind on machines with 50-in. wheels, while others, 

 who were not stronger riders, were travelling without 

 much difficulty on machines with 40-in. wheels. 



The truth is, that I have been advocating the use 

 of small wheels for years with a definite object in view. 

 I wished to see our machines combine the ease of the 

 bicycle with the comfort and safety of a tricycle. To 

 accomplish this, I saw that we must obtain a great reduc- 

 tion in their weight. We cannot dispense with the weight 

 of the third wheel and its friction on the road, but we 

 need have no more. When I began my experiments, 

 tricycles weighed about twice as much as bicycles. I 

 soon found that the greater part of the weight was in 

 the two driving - wheels. It was, therefore, absolutely 

 necessary to reduce the size of these if we wished to 

 make any considerable reduction in the weight of the 

 machine. This can be done without any disadvantage of 

 consequence, because the tricycle, unlike the bicycle, admits 

 of being geared up so that the pedals need not make a 

 greater number of revolutions with the smaller wheels. 



The driving-wheels must, of course, revolve oftcncr — let 

 them do so ; with ball-bearings tlie small additional friction 

 may be neglected. 



Some strong riders, I know, object to fast pedalling, Hnd 

 prefer to work with greater pressure on their pedals. This 



