206 



• KNOWLEDGE * 



[April 6, I883. 



walk up nearly all hills, and makes any tolerable 

 incline liarcl work. Very few riders care to have a 

 machine geared lower* than 48 in. ' The rapid motion 

 of their legs in pedalling, and the greater number of revo- 

 lutions the pedals have to make to cover a given distance, 

 tires them more than having to press harder on the pedals. 

 The proportion between the two speeds required by any 

 rider will, however, I think, be the same. This amount 

 will, I believe.'^be certainly not less than IG in., and not more 

 than 2."> in., and it will, I believe, in most instances be 

 about 20 in. 



For a double machine, in which one rider will probably 

 prove a weak driver, for instance, the two speeds will be 

 28 in. and 48 in., 30 in. and .'iOin., or 32 in. and 52 in. 

 For a single machine of rather strong build, weighing 

 about 1^0 lb., for a heavy, powerful man the proportions 

 n-ay well bo S.'i in. and •').5 in. ; while for a very light 

 roadster, weighing less than GO lb., the speeds, always 

 preserving the same proportion, may be 40 in. and GO in. 



By the kindness of Mr. Shaw I have had the advantage 

 of trying the Crypto-dynamic two-speed gearing. I tested 

 the machine at Surbiton, and I could not find any hill 

 steep enough to test the hill-climbing power of the machine 

 in the neighbourhood. The slow speed of this machine 

 was 22 in., and the high speed .'56 in. 



We are indebted to Grout for the first two-speed 

 gearing ; and with a perseverance which does him the 

 greatest credit, he has made successive improvements in 

 his gearing, and has latterly manufactured and introduced 

 a new contrivance by another inventor, which will probably 

 eclipse his own. The Crypto-dynamic gearing, to which I 

 have alluded, cannot, unfortunately, as yet be obtained. 

 This contrivance has successfully withstood some rough 

 work, and has certain special advantages peculiar to itself. 

 The two-speed contrivance of the St. George's Foundry 

 Company is worked by means of two chains, either of 

 which can be thrown in or out of gear at pleasure. This 

 contrivance possesses the great advantage that if either of 

 the chains should break, or the gearing get out of order, 

 the rider would be able to drive home with the other chain. 

 Britain's two-speed gearing seems to me the simplest, 

 and likely to weigh the least, and be the most economical 

 in price. Against these advantages we have to reckon two 

 drawbacks : the machine must always drive through the 

 gearing, so that it is always under strain ; and the gearing 

 cannot be thrown out of action so as to allow the pedals 

 to run free and act as foot-rests when running down hills. 



The various contrivances I have referred to could not 

 with advantage be described without drawings, and I have 

 said but little in this article as regards their details, or the 

 theories on which they are based. The reason I have 

 treated the subject in this manner is because I have 

 received numerous letters from readers of Knowledge, 

 asking me to make my articles on tricycles as practical as 

 I can. 



In one or two tricycling journals it has been suggested 

 that twelve inches would be a sufficient difference between 

 the high and low speed gearing. I do not think the 

 writers can have ridden with machines which have been 

 geared up and down more than this, or they would have 

 known that such a difterence wUl not give the full benefit 

 to be deri\ed from such a contrivance. For my own 

 riding I prefer 18 inches dill'erence to 20 inches. 



A suggestion also has been made that one of the two 

 speeds that is the fastest with the quick gearing, should be 

 exactly suited to the rider's general reijuirements, and the 

 slow gearing only brought into action for steep hills. 



This I cannot agree to. The result of such an arrange- 

 ment would be to give faster pedalling than is convenient 



to most riders, or a lower rate of speed than they might 

 easily obtain, both on the level and when riding up 

 ordinary inclines.^ 



A machine capable of being driven at two different 

 rates of speed, only with the same pedalling, should not 

 be geared down sufficiently to ride easily up a hill with a 

 rise of one foot in ten feet. The rider will gain greatly 

 by walking such a hill, and gearing his machine so as to 

 travel at a faster pace up a moderate rise. Steep hills 

 occur only seldom on most good roads, and occupy only a 

 very small portion of the ground to be covered, and nothing 

 is gained by toiling up at a slower pace than they can be 

 easily mounted by a good walker. 



THE AMATEUR ELECTRICIAN. 



ELECTRICAL MEASUREMENT.— IX. 



IN continuing our remarks on the Wheatstone Bridge, 

 we shall endeavour to show that in a given circuit the 

 fall of a potential varies as the resistance of the conductor, 

 and that this fact lends itself very opportunely to an in- 

 vestigation of the electrical conditions of a wire. 



Eirrh 



In Fig. 1 there are two wires (A B and E F) similar in 

 quality and cross-section, but unequal in length, A B being, 

 in this instance, half the length of E F. The potentials 

 at A and E (represented by A D and E G) are ob\-iously 

 identical, and B and F being to earth (Zero), it follows 

 that the fall from A to B is the same as that from E to F. 

 The fall in the circuit containing A B is, therefore, twice 

 as rapid as the fall in the other circuit through E F, 

 and the proportionate parts in each circuit will, there- 

 fore, be charged to the same potential, and so give 

 evidence of equal falls. For instance, H and K both 

 being one-fourth of the distance from A to B and E to F, 

 respectively, will be at the same potential represented by 

 the equal vertical lines H O and K P. So likewise will M 

 and L, three-fourths the distance from A and E, be at the 

 same potential, the vertical lines 51 R and L S being equal. 

 A gahanonieter inserted between H and K, or M and L, 

 would therefore remain passive and indicate the absence of 

 any current. As indicated in our preceding article, were H 

 joined to L (through a galvanometer), the needle would be 

 deflected, say to the right, by a current passing /Voh! H to 

 L. On the other hand, by joining H to any point between 

 E and K, say T, the current would flow to H from T, and 

 the needle would be deflected in the opposite direction — 

 that is, to the left. 



