There are fifty skilled men dotted about London, all holding certificates of proficiency in motor engineering, who exercise a constant surveillance. Quick of eye and keen of hearing, they keep unceasing watch on all public vehicles. An unusual sound as a motor omnibus passes may tell them something is wrong with the engine. Thereafter the proprietors are warned not to use the car until the defect has been remedied. Or they may station themselves unexpectedly at the gate of a garage, and test the brakes and steering gear of every car that passes in or out. That this is no mere formality is shown by the fact that on one morning an officer stopped no fewer than forty taxicabs from going on the streets. Indeed, during the last year for which figures are available officers of the department reported 35,123 vehicles as unfit for use. In some it was merely a question of noise or a trifling fault easily remedied. In others the trouble might easily have caused a bad accident. The principle acted upon throughout the department is that prevention is better than cure. Whenever a car of a new type is devised, be it a cab, an omnibus, or a tramway car, Scotland Yard examines it, and, if necessary, calls in a consulting expert for advice. Should the type be suitable, similar vehicles are afterwards examined by local staffs of the department--there are twelve of these in London--and a certificate presented by the maker that there has been no variation in the type. In the early days of motor omnibuses complaints in shoals were received by Scotland Yard from tradesmen, private individuals, borough councils, and others as to the frightful noises made by them when running. That resulted in the establishment of a committee of high executive officials for the testing of every motor omnibus in respect of noise before it is licensed. Pass through Great Derby Street into New Scotland Yard any day after ten o'clock, and you will find always a number of men clustered about a low building and in the little square. They are drawn from all types and classes, and all are candidates hopeful of obtaining their licences. A would-be taxi-driver--an "original" he is technically termed--has to be clean in dress and person and not under five feet in height. Two householders who have known him personally for three years must give him a good character. A doctor is required to certify that he does not suffer from any ailment, that he is sufficiently active, that he does not smoke or drink excessively, and that he is fitted for his duties by temperament. After this he will be permitted to undergo examinations in fitness and knowledge of driving. It is a tight-meshed net through which an incompetent would find it hard to pass.