1830.] 
On the Rent and Produce of Land . 
251 
1 y over them, at about ^d the length of the beam ; 5 blocks were also applied instead 
of three, as at first, viz. centre, 2 feet 7 inches ; 2 next, 2 feet 5 inches ; two 
end ones, 1 foot 5 inches. (Fig. 2.) The deflections were as follows: 
lbs. inches. 
150 ,125 
400 ,35 
700 ,6 
1000 ,9 
1350 1,2 
1500 1,4 
1600 1,5 
1700 1,65 
1900 2,0 
1961 2,4 
Broke near one of the fulcrums. 
No. 3. A specimen of similar dimension to the last, but scarfed in the centre, the 
joint being 6 inches in length, and secured by 2 small straps, was then put to the 
test, the scarf being placed vertically. This was similarly prepared with tie and 
blocks as on the last occasion, but 4 straps were intermediately applied instead of 2 
between the fulcra, and the specimen was, on the whole, more carefully secured 
than the entire pieces. (Fig. 3 and 4.) 
lbs. inches. 
150 ,1 
300 ,225 
450 ,375 
600 ,5 
1000 ,8 
1323 1,05 
1500 1,175 
1728 1,375 
1900 i,525 
2135 2,3 
Broke at the joint, in consequence of the splitting of the supporting block. 
No 4. Prepared similarly to No. 3, broke near the scarf, but clear of’ it, under 
a weight of lbs. 2147, deflection 2,15 inches; results so nearly resemblin’*- those 
detailed for No. 3, as to render insertion unnecessary. ° 
In almost all the preceding cases, great nicety in fitting on the parts was not 
attempted ; doubtless the resistance would, with greater care, have been greatly 
increased : yet these experiments, so far as they go^ tend to show the power of re- 
sistance, increased about 400 per cent, by the application of the iron ; a beam which 
by itself would certainly have yielded under a weight of 415 lbs. having succes 
sively sustained 1515 lbs., 1900 lbs., 2130 and 2140 lbs. From the above few 
experiments, the following conclusions may, I think, be drawn. 
1st. That security, as well as simplicity and economy, are likely to result from 
the adoption of this principle in large roofs ; which, when constructed with a con 
siderable pitch, expose so great a surface to the effects of heavy winds as to render 
their stability somewhat precarious, without a heavy expenditure of timber. 
2d. That if the iron tie be properly fitted, there should be no deflection whilst 
it continues perfect, the tendency to bend vertically being prevented by the sun 
porting tie, whilst lateral motion is precluded, by the arrangement of the burzahs * 
hence the peculiar applicability of this system for terraced roofs of large spans bv 
the security it gives against cracks, and the facility of using small sized timber.’ Y 
3rd. With beams loaded in the middle, it appears expedient to fill up with slio-ht 
materials, the whole of the space between the beam and its tie, in order to render 
it perfectly stiff. This precaution is obviously less necessary in cases of uniform 
VII . — On the Rent and Produce of Land. 
To the Editor of Gleanings in Science. 
Sir, 
A correspondent, under the signature M.,has, in the April number of the Glean- 
ings, mentioned, that it is a common practice of the landholders in his neighbour- 
