Cryptogram from Frankenstein; or, the modern prometheus, chapter 24

I mentioned in my last letter the fears I entertained of a mutiny. This morning, as I sat watching the wan countenance of my friend - his eyes half closed and his limbs hanging listlessly - I was roused by half a dozen of the sailors, who demanded admission into the cabin. They entered, and their leader addressed me. He told me that he and his companions had been chosen by the other sailors to come in deputation to me to make me a requisition which, in justice, I could not refuse. We were immured in ice and should probably never escape, but they feared that if, as was possible, the ice should dissipate and a free passage be opened, I should be rash enough to continue my voyage and lead them into fresh dangers, after they might happily have surmounted this. They insisted, therefore, that I should engage with a solemn promise that if the vessel should be freed I would instantly direct my course southwards.

The sentence you are solving goes here.

"What do you mean? What do you demand of your captain? Are you, then, so easily turned from your design? Did you not call this a glorious expedition? "And wherefore was it glorious? Not because the way was smooth and placid as a southern sea, but because it was full of dangers and terror, because at every new incident your fortitude was to be called forth and your courage exhibited, because danger and death surrounded it, and these you were to brave and overcome. For this was it a glorious, for this was it an honourable undertaking. You were hereafter to be hailed as the benefactors of your species, your names adored as belonging to brave men who encountered death for honour and the benefit of mankind. And now, behold, with the first imagination of danger, or, if you will, the first mighty and terrific trial of your courage, you shrink away and are content to be handed down as men who had not strength enough to endure cold and peril; and so, poor souls, they were chilly and returned to their warm firesides. Why, that requires not this preparation; ye need not have come thus far and dragged your captain to the shame of a defeat merely to prove yourselves cowards. Oh! Be men, or be more than men. Be steady to your purposes and firm as a rock. This ice is not made of such stuff as your hearts may be; it is mutable and cannot withstand you if you say that it shall not. Do not return to your families with the stigma of disgrace marked on your brows. Return as heroes who have fought and conquered and who know not what it is to turn their backs on the foe."