Boller was ‘an expert in bridge engineering and stood in the front rank of structural engineers of his day’ (DAB). In his ‘Practical Treatise’, he has attempted to provide a series of guidelines both for the local public committees responsible for the letting of contracts and for the engineers who, often with little experience in this field, were required to act as inspectors.The book is divided into two parts, of which the first is practical and concerned with the various types of bridge available; material; trusses; beams and columns; I-beams; struts and ties; decking; architecture; methods of construction and so on, taking as examples Boller’s own bridges and those of companies such as the Phoenixville Bridge Works. The second part is more technical, looking at stress; loading; neutral axis; bending moments etc. Throughout, Boller is much concerned with joints ("the essence of good bridge-building lies in their proper design") and includes a section comparing the English and American systems, much to the detriment of the English!