all should do) will devote both time and attention to the weighing of evidence. [19] The other error is that some people devote too much industry and too deep study to matters that are obscure and difficult and useless as well. If these errors are successfully avoided, all the labour and pains expended upon problems that are morally right and worth the solving will be fully rewarded. Such a worker in the field of astronomy, for example, was Gaius Sulpicius, of whom we have heard; in mathematics,