Mr. hunter on a new Method of applying the Screw. 59 - 
3. That the machine be as fimple as is confident with other 
conditions. 
4. That it be as portable and as little troublefome in the ap- 
plication as poffible. 
5. That the contrivance be fuch that the moving power 
may be applied in fuch a way as to acl to the greated 
advantage ; and that the motion ultimately produced may have 
that direction and velocity which is mod: adapted to. the execu- 
tion of the defign propofed by the whole. 
6. Of two machines, equal in other refpedts, that deferves 
the preference in which the fridtion leaf! diminifhes the effedt 
propofed by the whole. 
It will eafily appear, that fome of thefe conditions, if car- 
ried to an extreme, will be inconfiftent with fome of the others. 
Here the proper medium conffils in adapting them to each other 
in fuch a manner, as that the refult of the advantages of both 
may be the greateft, and that of the defedbs the leaft, that is 
poffible. 
The following method of applying the fcrew, I think, may 
in certain cafes be attended with fome of thefe advantages to a 
greater degree than by thofe commonly pradtifed. 
Let ab (fig. 1.) be a plate of metal in which the fcrew 
cn plays, having a number of threads in an inch equal to a. 
Within the fcrew cd there is a female fcrew, by which is re- 
ceived the fmaller icrew de of a 4 - 1 threads in an inch. This 
fcrew is retained from moving round along with the fcrew cp 
by means of the apparatus at afgb. 
Now, if the handle ckl be turned a times round the fcrew, 
CD will advance upwards an inch, and if we fuppofe the fcrew 
de to move round along with CD, the point e will alfo advance 
an inch. If we now turn the fcrew de a times backwards, the 
I 2 point 
