This is a very nice transit made by Young in Sons around 1890. I have an 1885 Y&S Catalogue on my website but the catalogue doesn't show very many transits. I put the pages from the best fit below. I suspect the Y&S product line evolved a bit from 1885 to 1890 or so, however. Take a look at the aluminum base of the transit offered here for example - none of the transits featured in the 1885 catalogue have that type of aluminum base.

The scope on this transit is roughly 9.25 inches, and it's a nice scope with good crosshairs. I note a bit of binding when the transit is rotated horizontally. The levels are good, however.

The verniers read to 1 minute.

I have a good deal of information about Young & Sons, including some production information, posted on my William Young Maker Webpage.

360 Degree Spinner View - With ZOOM View