relative to Experiments on Wheel-carriages. PI 



other, the curves and inequalities of these two paths were accu- 

 rately deiineared, and could be examined and compared at lei- 

 sure. 



Bv means of those contrivances various problems, relative t<;« 

 the motion of carriages and the effect of springs, may be resolved 

 at leisure, which could not, by any other means that I am ac- 

 quainted with, be subjected to accurate investigation. 



Upon the whole, I beg leave to observe, that the chief thing 

 to be attended to is, without any comparison, the goodness of 

 the road. 



That the difference in length and height of carriages, withia 

 moderate limits, does not much affect the draft of carriages. 



Thai carriages may therefore, except where they are obliged 

 to turn in narrow streets, be cf such a length as to permit th« 

 foremost wheels to lock round, without touching the body of the 

 carriage. 



That by lowering the centre of gravity of carriages, by placing 

 the luggage at the bottom of the carriage, the draft is not im- 

 peded, whilst great additional security is necessarily obtained. 



That no verv great saving of draft can be expected from the 

 different forms of axletrees. 



Thar every means of saving absolute weight, in the construc- 

 tion of a carriage, should be adopted. This caution will be at- 

 tended to bv every person who considers, that in going up a hilJ, 

 the ascent of which is one foot in twenty, the horses that draw 

 the carriage must exert a force equal to one-twenticlh part of 

 the weight of the carriage and of its load, which, in a common 

 stage-coach, is often equal to two hundred weight, and so in 

 proportion to the acclivity of any hill. 



That the application of springs to carriages, either for carryirii-; 

 burdens or for pleasure, tends not only to the ease of the tra- 

 veller, to the safety of goods that are carried, to the preservation 

 of the roads, and to the duration of carriages themselves, but 

 that they also materially facilitate their draft. 



That the form of those springs, provided thev are properly 

 elastic, is of no great consecjuence. By properly elastic, I mean 

 adapted to the medium weight with which it is proposed to load 

 them: for where the springs are strong, and the carriage not 

 sufficiently loaded, much of the advantage of springs is found to 

 be wanting. 



It is therefore much to be wished, that some means may be ob- 

 tained of proportioning the pliability of the springs to the different 

 weights with which they maybe loaded at different times. Who- 

 ever has travelled alone in a mail-coach has felt what I al- 

 lude to. 



And 



