158 THE LAW AFFECTING ENGINEEES 



glue in the manner required, and was useless for the purpose 

 of the business. It was argued that, upon the terms of the 

 contract, the plaintiff was bound to make a machine which 

 was efficient for the purposes of the defendant's business. 

 The Court, however, held that the approval was as to the 

 strength and workmanship, and not as to the efficiency of the 

 machine. 



18. Certificates and extras. As a general rule, the con- 

 tract provides that the employer shall only be liable to pay 

 for extras ordered by the engineer and included in his 

 certificate. For instance, a clause is generally inserted 

 to the effect that the contractor shall have no claim for 

 extra payment beyond the contract price in respect of any 

 work done by him for the corporation, unless previous to the 

 execution of the alterations he shall have received a written 

 order from the engineer expressly stating that the work is to 

 be the subject of an extra charge, and then only for the 

 amount which the engineer in his final certificate shall certify 

 to be due to the contractor in respect of such alterations and 

 additions (see, e.g., Form L, 01. 10, and Form IIA., 

 01. 13, post). The advisability of having an express pro- 

 vision on this question will be manifest. It may be 

 mentioned that where an architect or engineer gives his 

 final certificate in respect of a contract which includes extra 

 work, the final certificate is conclusive, and neither party can 

 raise the question whether or not there was a sufficient 

 order in writing (Goodyear v. Weymouth Corporation, 1866, 

 1 H. & K. 67). 



Where the contract contains no special provision for ordering 

 extras, but states that the contractor shall be paid for all 

 extras at the price fixed by the engineer, it seems that the 

 grant of a final certificate in respect of work that includes 

 extras, is conclusive. In such a case the engineer has power 

 impliedly to determine what are extras under the contract, 

 and his decision on the point cannot be called in question 

 (Richards v. May, 1883, 10 Q. B. D. 400). With this case, 

 however, should be compared the earlier decision in Tharsis 

 Sulphur Co. v. McElroy & Sons, 1878, 3 A. C. 1040, which 

 brings out the difference in this respect between a final and a 

 progress certificate. There the contract provided that there 

 should be no extras without the engineer's written order. It 



