Clockwise from 4 run three titles (6,2,3,6,7,9,3,4,3,4,5) linked with X who won a 21 of 8s. 29 is a fourth such title. Solvers must shade the three clued lights that combine to form an anagram of X (two words). 29th August is doubly significant.
 

Across

 
9    Sea lion’s grandchild swallowing salt (5)
10    Painter shed tears about China (5)
11    My railway truck (5)
12    Sewers trimmed cape Caesar shortened thrice (7)
13    Vent abuse together with spitfire (10, two words)
15    Keeper trailing black bear (5)
18    Alien badgers king and emperor (and the other folk) (8, two words)
19    Enlightenment transformed aristo (6)
24    Old romance clown talked about (5)
25    Force in support the English annihilated (5)
26    Tots are two daughters plus son (4)
28    Fireball was introduced to gambling game by rector (6)
34    Harmonize in time or tempo (5)
36    Working animal laden with junk (10, two words)
37    Despair no more, gripped by a new lively dance (7)
38    Fibre shown by temple priest keeping athletic (5)
39    God unknown in old kingdom (5)
40    Jack almost too much for pack of cards (5)
 

Down

 
1    Scent and sound of European river (5)
2    Scots wag hides neutron bomb in northernmost town (7)
3    Starers perturbed gentle sort (10)
4    Mellow horse carries workers (6)
5    Extinct ox died of nettle rash (5)
6    Delaware river delta cleared of mines (8)
7    River in Spain upset a fish (5)
14    PM departed towards Thule (5)
16    Thinking man dug earth out (4)
17    Criminal magistrate stalks (10)
20    Grievance exercises first lady (5)
22    Monkey nut poisoned ape hater (8, hyphened)
23    Fashion garment close to obscene (4)
27    Rodents relish needling sloths (7)
30    Nun (not base) minimal aberration rattles (6)
31    Lunacy cuckoo scholar conceals (5)
32    City of heroes unknown for ego (5)
33    Prince is after Aramaic tapestry (5)
35    Mary Jane’s canary (5)
 
A first prize of £30 for the first correct solution opened on 14 September. There are two runners-up prizes of £20. (UK solvers can choose to receive the latest edition of the Chambers Dictionary instead of cash— ring the word ‘Dictionary’.) Entries to: Crossword 2226, The Spectator, 22 Old Queen Street, London SW1H 9HP. Please allow six weeks for prize delivery.