If the technique, as you properly say, is for the most part dependent upon the state of science, then so much the more is science dependent upon the state and needs of technique. If society has a technical need, it serves as a greater spur to the progress of science than do ten universities. The whole of hydrostatics (Torricelli, etc.) was produced by the need of controlling the mountain streams in Italy in the sixteenth and seventeenth centuries. We only acquired some intelligible knowledge about electricity when its technical applicability was discovered. Unfortunately, in Germany, people have been accustomed to write the history of the sciences as if the sciences had fallen from the sky. So with all other accidents and apparent accidents in history. The further removed the field we happen to be investigating is from the economic, and the closer it comes to the domain of pure, abstract ideology, the more we will find that it reveals accidents in its development, the more does the course of its curve run in zig-zag fashion. But fit a trend to the curve and you will find that the longer the period taken, the more inclusive the field treated, the more closely will this trend run parallel to the trend of economic development. The greatest obstacle to the correct understanding of the theory in Germany is the irresponsible neglect of the literature of economic history. It is hard not only to get rid of historical conceptions which have been drummed into one s head at school but even more so to gather together the material necessary to do it. Who has even read, e.g., old G. v. G lich, whose dry accumulation of material nonetheless contains so much stuff which explains innumerable political facts? In addition I believe that the fine example which Marx himself gives in his Eighteenth Brumaire ought to give you considerable information on your questions just because it is a practical illustration. I also believe that in the Anti-D hring, ch.I, 9-11, and II, 2-4, as well as III, 1, or the introduction, and then in the final section of Feuerbach, I have already treated most of the points. I beg of you not to weigh gingerly each separate word of the above by itself but to take the connections into account. I am sorry that I have not the time to work things out and write you with the same exact detail that I would have to do for publication. Please pay my respects to Mr. ... and thank him for me for sending along the ..., which cheered me up greatly. 
Letters: Marx-Engels Correspondence 1894