The question raised by the appeal is whether it was the legal duty of the respondent, when required by the appellant, to assess the duty on the transfer at the amount which a calculation on that basis would produce. It is the duty of the respondent, under the Stamps Act, to assess the amount of duty which is chargeable, according to the true intention of the Act, on such instruments as are dutiable. But, the question of determining what that amount of duty is, the Act leaves to the opinion of the collector, subject to an appeal, in the form provided by the Act, to the Supreme Court. It would be inconsistent with the legislative scheme for assessing and reviewing the assessment of instruments which are chargeable with duty for the court to inquire on mandamus what is the amount of duty payable on an instrument and to compel the collector to assess the duty at that amount. His statutory duties are peculiar. When an instrument is lodged to be stamped, he is required to express "his opinion" on the question whether it is chargeable, and, if, in his opinion, it is, with what amount of duty, and to assess the duty at the amount with which it is, in his opinion, chargeable (sec. 32). The result of the performance of these duties, which mandamus would lie to enforce, is that the amount of duty to which an instrument is liable is assessed in due course of law; the Supreme Court may review the assessment in the manner provided in sec. 33. It is not a necessary element in the performance or the collector's duty to give an opinion which the court would consider to be correct. The duty imposed on him is to express "his opinion"; and he performs this duty whether his opinion is right or wrong. The court will not on mandamus dictate to the respondent the opinion he must give on any of the questions which the Act leaves to his judgment. The mandamus sought would compel the respondent to make an assessment of an amount of duty which is not shown to be the amount with which, in his opinion, the transfer is chargeable. It would compel him rather to act at variance with his statutory duty than to perform it; for the mandamus, if issued, would compel him to assess the duty chargeable on the transfer at an amount less than that which it is, in his opinion, liable to bear.