Shown at the Great Exhibition of 1851, the Alexander Dalgety lathe was listed in the condensed catalogue in Class VI as exhibit No. 206: "Dalgety, A. Deptford, Inv. And Manu.- Self-acting and surfacing and screw-cutting lathe, self-adjusting chucks, etc," The fuller catalogue provides a few more details: Self-acting and screwcutting lathe, with a set of eighteen gun-metal change wheels, for screw cutting from three threads in a foot , to 95 in an inch.
Self-adjusting chuck, with three jaws always working parallel to each other, for fixing any sized wire perfectly central, from the smallest  needle to a bar 1 inch in diameter, particularly adapted for holding drills of various sizes, and making small screws [the latter almost certainly referring to the 3-jaw chuck shown below].
Self-adjusting boring collar, for supporting various sized bars or tubes , from 1/8-inch to 21/2-inches in diameter [instead of the contemporary type of fixed steady with a rotating disc bored with a series of different diameter holes, might this have been identical to the modern fixed steady with its three radial and adjustable sliding supports?]
Self-adjusting face chuck, for holding circular flat surfaces from 3/8-inch to 7 inches in diameter [could this refer to a modern-style self-centring 4-jaw chuck?].
Although the surviving lathe shown below is of the simple, plain-turning type and so lacking power feed along the bed and screwcutting, the two chucks are indeed of the "self-adjusting" type i.e. what would now be called self-centring.  Of unusual but very graceful appearance, the 3-jaw was constructed from bronze and steel and had an evidently superb cosmetic finish. Of what is now termed a "ring-scroll" type, the inner face of a peripheral ring acted directly upon the rim of the scroll used to move the jaws to move in and out, the mechanism being turned by a bar inserted into one of three holed drilled into the body. This design, largely confined to lighter types of chuck, survives to this day for use on high-precision miniature lathes, the outer ring usually being knurled for finger grip and sometimes also fitted with Tommy-bar holes.
The 2-jaw chuck used key operation, the square-headed bolt to take the key being nearly recessed into the body--unlike some dangerous contemporary versions that had the bolts heads protruding and ready to catch an unwary hand or sleeve.
With a triangular bed the lathe exhibits many features typical of light lathes made in the period from 1800 to around 1870. Triangular beds were a relatively common type (even the original screwcutting-by-changewheels lathe of Richard Maudslay c 1800 being of this type) with the Boley and Glashütte in Germany, Prudor and Strube & Fils in France and CLH in England all employing the design on lathes intended for use by watch, clock and instrument makers.
Although now lacking the fitting, it's likely that the Dalgety would have been available with a compound screw-feed slide rest assembly to mount in place of the hand T-rest. Many decades ago the writer owned a very similar plain-turning lathe with (from memory) identical support feet. Last heard of in Ilkeston, Derbyshire, this lathe had a full screw-feed slide rest of most ingenious design and may well have been, upon reflection, a Dalgety..