Was the Coanda effect known in 1868 to Matthew Piers Watt Boulton (the one who described the first ailerons)?
The accompanying text clearly describes an application of the Bernoulli effect. However the resultant backwards airflow shown in the drawing is given no explanation, other than that implied by the fact that the device is drawn forwards. So there is no evidence of the Coanda effect, in which the airstream clings to the device skin, being understood.
Would it have worked? Probably, but it would have been pretty inefficient.