This study guide introduces Second Scientific Lecture-Course: Warmth Course (GA 321), a series of fourteen lectures Rudolf Steiner delivered in Stuttgart between 1 and 14 March 1920. Addressed largely to teachers and to people working out a science curriculum for the first Waldorf school, the course takes up the physics of heat as its central subject. Steiner treats warmth not as a side effect of moving particles but as a phenomenon worth studying in its own right, beginning from ordinary sensation and the behaviour of the thermometer and building toward a wider picture in which the states of matter, the action of the sun, and the very boundary between the physical and the non-physical all come into view. It is the second of two scientific courses he gave for educators, following the Light Course of 1919, and it remains one of the most concentrated statements of his approach to natural science.
Place in Steiner's Work
By 1920 Steiner had spent two decades developing anthroposophy as a path of inner training, and he had begun applying its method to practical fields: medicine, agriculture, education, and the sciences. The Warmth Course belongs to that applied turn. The first Waldorf school had opened in Stuttgart in September 1919, and its teachers needed a way of presenting physics that did not simply hand pupils the inherited materialism of the textbooks. Steiner offered these lectures partly as raw material for that task.
He situates the course as a continuation of the earlier light lectures, and he is explicit that he wants to lay a sound foundation for a scientific world view rather than to overthrow experiment. What he criticises is not measurement but the habit of explaining everything by hidden particles and abstract formulae. He traces this habit historically to the Italian experimenters of the seventeenth century, the Academia del Cimento, and argues that an older, more cosmic way of thinking was lost in the years between the fifteenth and seventeenth centuries. The course thus sits at the meeting point of Steiner's epistemology, his history of science, and his educational reform.
The Warmth Course also marks a stage in Steiner's long argument with the dominant science of his day. He had been making the case since the 1880s, in his work on Goethe's scientific writings, that nature can be known through careful observation of phenomena rather than through models built behind them. In 1920 he brings that conviction to bear on thermodynamics, one of the proudest achievements of nineteenth century physics. The setting matters too. These were not lectures for a general audience but working sessions for teachers, given in the same Stuttgart in which the Waldorf school had just begun, and they were accompanied by demonstrations and by contributions from colleagues such as the physician Eugen Kolisko. Readers should approach the text as a record of that practical, collaborative effort rather than as a finished treatise.
Themes and Structure
The fourteen lectures move steadily outward from the familiar to the unexpected. Steiner opens with the subjectivity of warmth: the same water feels warm to one hand and cool to the other, and as he puts it,
Heat is first known through sensations of cold, warmth, lukewarm, etc.
From there he turns to the thermometer and the measured expansion of solids, liquids, and gases under heat. The early lectures establish the experimental ground carefully, with iron rods, coloured liquids, and the standard expansion coefficients of physics, so that nothing in the later argument floats free of observation.
The pivot of the course is Steiner's treatment of the three ordinary conditions of matter. As bodies pass from solid to liquid to gas, he observes, their individual properties fall away and a kind of unification sets in: gases of every substance behave much alike, while solids are sharply differentiated. He links this to the old Greek vocabulary, in which solid was called earth, fluid water, and gaseous air, and he reads those words as pointing to the forces that govern each condition. Solids, on this view, obey the laws of the earth; fluids answer to the wider planetary system; gases stand under the unifying action of the sun. The lesson he draws is methodological as much as physical: a science that explains the sun in earthly terms has things backwards and should instead read the earthly in cosmic terms.
In the middle lectures Steiner extends the same logic to the boundary cases of physics. He works with the distinction between ordinary weighable substance and the lighter agencies that act through it, asking where heat, light, chemical effect, and tone belong on that scale. Some of these agencies bind tightly to matter and seize directly on it; others remain comparatively free, accompanying matter without merging into it. Steiner uses this difference to characterise such phenomena as chemical combination, which works upon the fluid element, and tone, which he treats as preserving a certain independence within the air. The point is to show that the line between the weighable and the unweighable is not a wall but a graded boundary that physics can study attentively.
The closing lecture gathers the threads into a layered scheme. Steiner lists five orders of reality that the course has touched: the solid, the fluid, the gaseous or aeriform, the order of chemical effects, and finally the order of life. He shows how each works into the others, so that chemistry, for instance, appears as the fluid element animated by chemical activity. He then sketches a striking analogy between the periodic arrangement of the elements and the octaves of music, suggesting that the building and breaking of compounds reflects an inner ordering comparable to the intervals of tone. Throughout, the structure is cumulative rather than systematic: each lecture adds a fact and a question, and the reader is asked to hold the whole picture in mind rather than to memorise results.
What unites the fourteen lectures is a single methodological demand. Steiner asks the student to begin from what can be shown and measured, then to resist the temptation to fill the gaps with invented particles. Where the textbooks reach for hidden mechanisms, he reaches for the wider context in which a phenomenon stands, whether that is the planetary surroundings of a melting solid or the cosmic origin he assigns to tone. The course is therefore as much a training in scientific attention as it is a treatment of heat.
Glossary Terms from this Volume
Several entries in the Thalira glossary draw directly on GA 321. This page serves as a hub for those terms, each of which develops a concept the Warmth Course opens up:
Where to Read It
You can read the full text of the Warmth Course in English at the Rudolf Steiner Archive, where the fourteen Stuttgart lectures are freely available alongside the German original. For print editions and related scholarship, search the catalogue of the publisher at SteinerBooks. Reading the lectures in sequence is worthwhile, since the argument is built step by step from the opening experiments to the closing synthesis.
Continue Your Study
The Warmth Course rewards study alongside Steiner's wider thought. To go further:
- Browse the full Thalira glossary to see how the physical concepts of GA 321 connect to terms across his work.
- Begin with The States of Aggregation, the idea around which the whole course turns, then follow it into the more demanding notions of Ponderable and Imponderable Matter and Negative Space and Suction Forces.
- Read the lectures with pencil in hand, sketching the expansion diagrams and the layered scheme of orders for yourself, as Steiner intended them to be used in teaching.