Никогда не видел такой конструкции. Кто-нибудь знает, как она работала?

>Четырёхосный моторный Jones Type 1

Всё же трёхосный ;)

Крайние оси, скорее всего, на одноосных поворотных тележках. А вот на колёсах средней оси, по-моему, совсем нет реборд. Посмотреть бы кинематическую схему.

Скорее, средняя ось, сдвигаясь строго поперёк кузова в кривой, аккуратно направляет поворотные крайние, давая лучшую вписываемость в повороты.

Жёсткая опорная средняя ось с колёсами без реборд на городских трамваях маловозможна, ибо в кривых малого радиуса может "спотыкаться" во внутреннем выносе о булыжник или другие неровности мостовой, находящиеся выше УГР. Это было бы слишком чревато сходами.

Да, пожалуй, вы правы. Скорее всего средняя ось имеет значительный поперечный разбег. Но взглянуть на кинематическую схему мне всё же хочется.

Here is a description by the West End Railway of the 3 axles trucks:
"Manufactured by the Robinson Radial Truck Co., with improvements made by the railway company in some details, and used under 25 ft. box cars or long open cars. There are three trucks in one, , or three axles with frame about them, all tied together with pin connections as well as by the brake mechanism and the end frames and axles, being pivoted at their centers to the car body. The centre frame and axle always stands and moves at right angles to the longitudinal axis of the car.
The end axles are 14 ft. on centers. Each end truck is intend to carry 2/5 of the whole load.
They consist of an irregular oval shaped frame of channel iron, carrying the four corner chafing rollers, the two jaw castings, the brake mechanism and supports for the motor and fenders. Intermediate cross bars in the frame carry the center castings with roller bearing attached to an idle frame. The center truck frame is similar but smaller and arms on each engage the arms of the end trucks above swiveling pins.
Saddles are placed over each box to carry the springs and held support the fenders. One motor is used on each end truck only.
The Railway Company’s standard brake shoes, axles, fenders and bearings are used. There are 51 trucks of this class.
These trucks were purchased during 1890 and 1891 and at the present time are so badly worn that it has been thought advisable to discard this pattern and twenty-seven were destroyed shortly after the lease (to the Boston Elevated Railway) went into effect."

Thank you very much!

What is mean: "all tied together with pin connections ..."?

Видимо, "связаны/соединены тягами".