most prolific source of hot boxes. The weight per square inch upon the
bearing is a very important factor. I have found by careful
examination of a great many cars that the number of hot boxes bears a
close relation to the weight per square inch on the journal and the
character of lubrication, and is not so much affected by the size of
wheel or speed. These observations were made upon 42 in., 36 in. and
33 in. wheels in the same trains. We find, furthermore, that while a
3-3/8 in. journal on a 33 in. wheel is apt to heat under our passenger
coaches, a 33/4 in., even when worn 3-5/8 in., journal on a 36 in. wheel
runs uniformly cool. In 1890 on one division there were about 180 hot
boxes with the small wheel, against 29 with the larger one, with a
preponderance of the latter size in service and cars of the same
weight over them.

I do not know that there is any more tendency for a large wheel to
slide than a small one under the action of the brakes, but large
wheels wear out more brake shoes than small ones, if there is any
difference in this particular.

My conclusions are that 42 in. is too large a diameter for steel
wheels in ordinary passenger service, and that 36 in. is right. But as
steel-tired wheels usually become 3 in. smaller in diameter before
wearing out, the wheel should be about 38 in. in diameter when new.
Such a wheel can be easily put under all passenger cars and will not
have become too small when worn out. A great many roads are using 36
in. wheels, but when their tires have lost 3 in. diameter they have
become 33 in. wheels, which I think too small.

There are many things I have left unsaid, and I am aware that some of
the members of the club have had most satisfactory service with 42 in.