What, then, is the function of this picture for scientists? It is to stimulate the individual specialist to clarify for himself his expectations about the future, as a guide to the timing of scientific work.
A developmental construct, then, is a very odd kind of vision of the future. Lasswell says it may not even be the most likely expectation, as long as it is a "total" one rather than a mere extrapolation of trends into the future. So the key here seems to be two-fold: a developmental construct is a more or less complete picture, and it is a picture that is both grounded in empirical observation of contemporary possibilities and in a set of values one wishes to preserve. Indeed, part of what makes the garrison state work as a vision of a future to be avoided is that Lasswell is writing to an audience of democratic citizens, citizens who can be expected to react strongly and negatively to the brave new world he's sketching out. Take away either the empirical observations or the audience's value-commitments, and the picture ceases to be as alarming as Lasswell obviously intends it to be.
Lasswell's pretty clear; H. G. Wells, not so much. There's a point on p. 114 when he has his narrator invite the listeners -- including, presumably, the reader -- to take the story as something like one of Lasswell's developmental constructs: "Consider I have been speculating upon the destinies of our race until I have hatched this fiction. Treat my assertion of its truth as a mere stroke of art to enhance its interest. And taking it as a story, what do you think of it?" But at the same time, Wells' novel takes pains to ground the tale of the future of humankind in a whole series of empirical and scientific observations: the discussion of time as a fourth dimension, the detailed descriptions of the machine and the Time Traveler's house, even the mysterious ending-line before the Epilogue which purports to be relating what "everybody knows now."
So here's my question: do these elements of narrative in Wells' novel make his future more or less believable than Lasswell's? Should Lasswell, perhaps, have just written a novel instead?