150 
Again, Mr. Houldsworth’s beautiful differential motion, then 
called “Jack in the box,” being governed by bands and 
pulleys, their chance of slippage rendered it desirable to sub- 
stitute toothed wheels, on which occasion Mr. John Kennedy 
and Mr. Peter Ewart each discovered the three-wheel motions 
since adopted — those of Mr. Ewart were mitre wheels, Mr. 
Kennedy’s, spur gearing — the latter being mostly preferred. 
And it is worthy of note that the three mitre wheels for 
giving the differential motion in the slide lathe, required for 
turning cones, had been long in use and publicly seen with- 
out any one having dreamed of the application of them to 
other objects ; nor was Mr. Houlds worth at all aware of these 
slide lathe differentials until pointed out to him by Mr. 
Ewart. 
The paper concludes by an earnest appeal to Mr. Houlds- 
worth and other eminent mechanicians personally connected 
with the progress of modern inventions and improvements of 
the machinery employed in our manufacturing establish- 
ments, to record their own experience and observations upon 
the several branches with which they have been more espe- 
cially conversant, as has been done by Dr. Fairbairn in his 
published works, and as the author of these Notes has aimed 
to do. 
The following papers were read at the Photographical 
Section Meeting, February 8th, 1866. 
“On the Supposed Photographs by Boulton and Watt.” 
By Joseph Sidebotham, Esq. 
About three years ago the scientific world was startled by 
the announcement of the discovery of sun pictures, on paper 
and on silver plates, said to have been produced at the close 
