Thomas Hardy’s Two on a Tower was conceived to set two intimate human biographies against the immensity of the stellar cosmos, insisting that private affections can be the greater reality for individuals. Set in rural Wessex, its central locus is Rings‑Hill Speer, a pine‑clad round hill crowned by an eighteenth‑century Tuscan column that Swithin St. Cleeve uses as a private observatory. Astronomy is not mere decoration: it shapes character, supplies recurring metaphors, and structures the moral choices of the protagonists.

Principal figures
- Lady Viviette Constantine: an emotionally starved but wealthy woman rendered socially and financially precarious by her absent husband, outwardly powerful yet inwardly vulnerable.  
- Swithin St. Cleeve: the curate’s son, handsome, idealistic, and devoted to astronomy; a talented youth whose private observatory and equatorial instruments, publicly attributed to him, advance his scientific promise.  
- Secondary figures: Louis Glanville (Viviette’s worldly brother), Mr. Torkingham (the kindly parson), Mrs Martin (Swithin’s grandmother), Bishop Helmsdale, village characters and local labourers.

Narrative arc (compact)
Chance meetings on the column kindle a relationship: Viviette, fascinated by Swithin’s earnestness, becomes his secret patron—equipping the observatory while insisting the gift appear to come from Swithin to avoid scandal. Their intimacy deepens into clandestine marriage, contracted because social convention and age and rank make public union perilous. Swithin’s career advances—near discoveries, obsessive nights, a broken object‑glass replaced by Viviette—yet he suffers reversals and rival claims; celestial events (a comet) periodically reinvigorate his hope.

The novel’s closing episodes converge legal formality, conditional legacy, and sacrificial love into tragic irony. A late newspaper dispatch and the arrival of Sir Blount’s papers reveal that Viviette’s first husband died only recently; legally her marriage to Swithin is void and must be repeated. At the same time Swithin stands to inherit an annuity of £600 a year conditional upon remaining unmarried until twenty‑five—an instrument intended to secure his scientific future. Viviette, recognizing that formalizing the marriage will strip him of the income needed to pursue astronomy, elects sacrifice: she dissolves their intimacy, bids him travel and accept work abroad, and forbids contact. Swithin departs for distinguished work at Greenwich, the Cape, and America.

Viviette, isolated and brooding, is pressed into a pragmatic marriage with Bishop Helmsdale—an escape from scandal and mental torment rather than a romantic union—and later becomes his widow. Years on, a final reunion on the old column yields passionate reconciliation but proves fatal: the shock of regained joy kills Viviette in Swithin’s arms. Hardy frames this outcome with psychological realism and moral ambiguity: noble self‑denial secures a vocation yet exacts the most tragic personal price, underlining the tension between public duty and private fidelity against a cosmos whose immensity dwarfs human schemes.