3B6 REPOfiT— 1903. 



stream-line How was kept perfectly symmetrical about the constriction, 

 and hence the true mean pressure was recorded. 



Mr. Mallock has suggested the adoption of a length of resistance 

 tubing (say 1/60 inch bore) to attain the same end, and this will be fitted 

 for subsequent trials. 



Edperiimnts. 



The first experiments conducted with this dynamometer were men- 

 tioned in the last report and the results were indicated by means of wall 

 diagrams. The results then obtained have been carefully gone into and 

 from them the following curves have been plotted. 



Experiments with Iron Tyres. 



These experiments were conducted on a portion of Regent Road, 

 Bootle, which is paved with setts 6 inches by 3 inches, having a regular but 

 fairly rough surface, with a 1-inch gap between the joints. Regent Road 

 runs along the line of docks, and is in consequence free from gradients ; 

 it is, however, so crowded with vehicles during the day-time that it was 

 found necessary to conduct this series of experiments during the night. 



The wheel used was a light lurry-wheel, 40 inches diameter, having a 

 3-inch iron tyre slightly rounded in section. 



The axle was tilted up out of the horizontal at one end so that the 

 wheel — which was slightly coned — could take up a position exactly 

 similar to the lurry wheels in general use ; it Avas mounted on a pair of 

 springs 3 feet 2 inches between the centres of attachment, each spring 

 comprising six plates 2j inches by -{\. inch. 



Three runs were made over this particular route with loads of 392,. 

 672, and 952 lb. respectively, at speeds of from 5 to 14 miles per hour. 



The results of these trials are plotted in fig. 1, with total tractive 

 effort (inclusive of axle friction, Ac), as ordinates, and velocity as abscissaj. 



It will be noticed that for each curve the tractive effort increases 

 with the velocity, but these curves and all subsequently obtained are 

 concave downwards, showing that the rate of increase of tractive effort 

 diminishes with the, velocity. This may be due to the fact that as the 

 Avheel travels faster it has less time to fall into the little hollows in the 

 roadway, merely skimming along the tops of the ridges. 



Well-laid setts under these circumstances, even with wide deep gaps, 

 form a perfectly smooth track at high speeds. This is well brought out 

 in fig. 4, which shows a smaller tractive effort for setts than for macadam. 



On looking into the matter, this is as it should be. Consider two 

 perfectly level roads, one made with setts and the other with macadam : 

 the setts present a surface which is extremely hard, although irregular, 

 but this irregularity with well-laid setts is more apparent than real, as the 

 tops of the setts themselves are smooth and level and all in the same plane. 



The macadam, on the other hand, although quite level, is not nearly 

 so hard as the stone surface, and is, moreover, covered with a thin layer 

 of dust or fine gravel, which, as is well known, retards the progress of a 

 vehicle. 



Experimejits with Pneumatic Tyres, 



A series of experiments were made with a pneumatic-tyred wheel' 

 24 inches diameter, 2|-inch tyre. This Avas a wire-spoked wheel of the 

 type used on light voiturettes ; it Avas mounted on the same springs aS' 



